Add a space before build tag comments so it corresponds to the format
documented at https://golang.org/pkg/go/build/.

Change-Id: I8349d0343597e304b97fb5479847231ed8945b1a
Reviewed-on: https://go-review.googlesource.com/c/go/+/193237
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The exception allowed a specific intermediate [1] to chain up to a
broken root that lacked the CA:TRUE X509v3 Basic Constraint.

The broken root [2] is expiring at the end of 2019, so we can remove the
exception in Go 1.14.

Moreover, there is a reissued version of that root [3] (same Subject and
SPKI, valid CA) which expires in 2029, so root stores should have
migrated to it already, making the exception unnecessary.

[1]: https://crt.sh/?caid=57
[2]: https://crt.sh/?id=1616049
[3]: https://crt.sh/?id=55

Change-Id: I43f51100982791b0e8bac90d143b60851cd46dfc
Reviewed-on: https://go-review.googlesource.com/c/go/+/193038
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Right now we generate hash functions for all types, just in case they
are used as map keys. That's a lot of wasted effort and binary size
for types which will never be used as a map key. Instead, generate
hash functions only for types that we know are map keys.

Just doing that is a bit too simple, since maps with an interface type
as a key might have to hash any concrete key type that implements that
interface. So for that case, implement hashing of such types at
runtime (instead of with generated code). It will be slower, but only
for maps with interface types as keys, and maybe only a bit slower as
the aeshash time probably dominates the dispatch time.

Reorg where we keep the equals and hash functions. Move the hash function
from the key type to the map type, saving a field in every non-map type.
That leaves only one function in the alg structure, so get rid of that and
just keep the equal function in the type descriptor itself.

cmd/go now has 10 generated hash functions, instead of 504. Makes
cmd/go 1.0% smaller. Update #6853.

Speed on non-interface keys is unchanged. Speed on interface keys
is ~20% slower:

name                  old time/op  new time/op  delta
MapInterfaceString-8  23.0ns ±21%  27.6ns ±14%  +20.01%  (p=0.002 n=10+10)
MapInterfacePtr-8     19.4ns ±16%  23.7ns ± 7%  +22.48%   (p=0.000 n=10+8)

Change-Id: I7c2e42292a46b5d4e288aaec4029bdbb01089263
Reviewed-on: https://go-review.googlesource.com/c/go/+/191198
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Martin Möhrmann <moehrmann@google.com>

Change-Id: I3340561c0b17bf28d8d480e00f5bc8afb2a897ef
Reviewed-on: https://go-review.googlesource.com/c/go/+/193041
Run-TryBot: Andrew Bonventre <andybons@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>

Updates #31563
Fixes #34041

Change-Id: Ib9fdcd2f83d867fd31b42eab3a813f5cef88860e
Reviewed-on: https://go-review.googlesource.com/c/go/+/193077
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

The distribution of hash outputs when varying the seed is
not good enough on 32-bit platforms.

This isn't a likely attack vector (the adversary controlling the seed),
so it isn't a huge deal. Would be nice to fix, though. For now, just
skip this test.

Fixes #33988

Change-Id: Icf51ab687fc215422a5492ae78e6f414b33e04cb
Reviewed-on: https://go-review.googlesource.com/c/go/+/193078
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Assinging to 1-element array/1-field struct variable is considered clobbering
the whole variable. By emitting OpVarDef in this case, liveness analysis
can now know the variable is redefined.

Also, the isfat is not necessary anymore, and will be removed in follow up CL.

Fixes #33916

Change-Id: Iece0d90b05273f333d59d6ee5b12ee7dc71908c2
Reviewed-on: https://go-review.googlesource.com/c/go/+/192979
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

Fix a buglet in abbrev processing related to DW_FORM_indirect. When
reading an abbrev entry if we encounter an attribute with form
DW_FORM_indirect, leave the class as ClassUnknown, then when the
abbrev is walked during the reading of the DIE fill in the class based
on the value read at that point (code for handling DW_FORM_indirect
seems to be already partially in place in the DIE reader).

Updates #33488.

Change-Id: I9dc89abf5cc8d7ea96824c0011bef979de0540bf
Reviewed-on: https://go-review.googlesource.com/c/go/+/190158
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

In general, a conversion to interface type may require values to be
boxed, which in turn necessitates escape analysis to determine whether
the boxed representation can be stack allocated.

However, esc.go used to unconditionally print escape analysis
decisions about OCONVIFACE, even for conversions that don't require
boxing (e.g., pointers, channels, maps, functions).

For test compatibility with esc.go, escape.go similarly printed these
useless diagnostics. This CL removes the diagnostics, and updates test
expectations accordingly.

Change-Id: I97c57a4a08e44d265bba516c78426ff4f2bf1e12
Reviewed-on: https://go-review.googlesource.com/c/go/+/192697
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

While here, change the params to be easier to understand: "t" is now
always the type being updated, and "underlying" is now used to
represent the underlying type.

Updates #33658.

Change-Id: Iabb64414ca3abaa8c780e4c9093e0c77b76fabf9
Reviewed-on: https://go-review.googlesource.com/c/go/+/192724
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Robert Griesemer <gri@golang.org>

This CL extends {defer,resume}checkwidth to support nesting, which
simplifies usage.

Updates #33658.

Change-Id: Ib3ffb8a7cabfae2cbeba74e21748c228436f4726
Reviewed-on: https://go-review.googlesource.com/c/go/+/192721
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Robert Griesemer <gri@golang.org>

Change-Id: I6e9d47865c198299d497911c58235cd40f775e34
Reviewed-on: https://go-review.googlesource.com/c/go/+/175138
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

Also add a few other missing constants.

Also rerun current version of stringer.

Change-Id: I004ef27f6b40fe2cab64c52d169255dfea43fa01
Reviewed-on: https://go-review.googlesource.com/c/go/+/175137
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

This CL implements one lock per order of stackpool. It improves performance when mutator stack growth deeply, see benchmark below:

```
name                old time/op  new time/op  delta
StackGrowth-8       3.60ns ± 5%  3.59ns ± 1%    ~     (p=0.794 n=10+9)
StackGrowthDeep-8    370ns ± 1%   335ns ± 1%  -9.47%  (p=0.000 n=9+9)
StackCopyPtr-8      72.6ms ± 0%  71.6ms ± 1%  -1.31%  (p=0.000 n=9+9)
StackCopy-8         53.5ms ± 0%  53.2ms ± 1%  -0.54%  (p=0.006 n=8+9)
StackCopyNoCache-8   100ms ± 0%    99ms ± 0%  -0.70%  (p=0.000 n=8+8)
```

Change-Id: I1170d3fd9e6ff8516e25f669d0aaf1861311420f
GitHub-Last-Rev: 13b820cddd8008079c98d01ac22dd123a46a6603
GitHub-Pull-Request: golang/go#33399
Reviewed-on: https://go-review.googlesource.com/c/go/+/188478
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

Change-Id: I4e7b0e99fd0f6f7d6a8ef60e9d3cb5baeb80a2b6
Reviewed-on: https://go-review.googlesource.com/c/go/+/191617
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Those configurations currently lack builders, and it is not clear to
me what state their tests are in.

The Go porting policy¹ requires builders for all active ports, so
let's not claim support until that requirement is met.

¹https://golang.org/wiki/PortingPolicy#requirements-for-a-new-port

Updates #30824
Updates #31656
Updates #34035
Updates #34036

Change-Id: I6496de9d92fb8546048abf139cf10546a47e314b
Reviewed-on: https://go-review.googlesource.com/c/go/+/192997Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

This reverts CL 191759.

Reason for revert: broke most Go programs using the time package on Wine,
including on 4.15, the latest stable version. Only wine-staging (with
experimental patches) contains an upstream fix we could rely on.

Change-Id: Ic8ba126022e54f412174042fbb9abed82d5eb318
Reviewed-on: https://go-review.googlesource.com/c/go/+/192622
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

Change-Id: Icf7e1dab82aa48cc693eb4da8a564dff23312741
Reviewed-on: https://go-review.googlesource.com/c/go/+/192745
Run-TryBot: Andrew Bonventre <andybons@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

Fixes #33954

Change-Id: Idfe71bf825adcd7cbf70cd139b3e779963394ff6
Reviewed-on: https://go-review.googlesource.com/c/go/+/192105
Run-TryBot: Andrew Bonventre <andybons@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>

These changes make cmd/doc -src deterministic, or, more precisely,
go/ast.MergePackageFiles, which is used by cmd/doc. So far the order of
comments depended on the package file map iteration order.

cmd/doc with -src flag has been inserting and omitting random comments
ever since the addition of -src flag. After investigating the code path
with the debugger, I’ve noticed that ast.File.Comments slice order changes
between invocations of the command. The bug was introduced in 3e24f2d6,
which ironically claimed to “fix formatting of -src output”. The commit
implemented the collection of comments by iterating over the map and
c7cdce13 “godoc: make ?m=src mode deterministic” did’t actually make
go/ast.MergePackageFiles deterministic.

I’ve found this issue after running “go doc -src sync.WaitGroup.Wait”.
There are likely other packages and functions affected, but the bug
should be somewhat reproducible across all Go versions.

Change-Id: Iae223e99550c0a3b54005c5cde36f909e655b66b
GitHub-Last-Rev: c49532f79fcd7529d7ad1a369c467abc59d4df0a
GitHub-Pull-Request: golang/go#33553
Reviewed-on: https://go-review.googlesource.com/c/go/+/189477
Run-TryBot: Agniva De Sarker <agniva.quicksilver@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

Fixes #33743.

Change-Id: I80621321d56b6cf312a86e272800f1ad03c5544c
GitHub-Last-Rev: d91cb3697516ccfc3f956e97837404cbfee5922f
GitHub-Pull-Request: golang/go#33856
Reviewed-on: https://go-review.googlesource.com/c/go/+/191879
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

Some were never used, and some haven't been used for years.

One exception is net/http's readerAndCloser, which was only used in a
test. Move it to a test file.

While at it, remove a check in regexp that could never fire; the field
is an uint32, so it can never be negative.

Change-Id: Ia2200f6afa106bae4034045ea8233b452f38747b
Reviewed-on: https://go-review.googlesource.com/c/go/+/192621
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: Ib637381ab8a12aeb798576b781e1b3c458ba812d
GitHub-Last-Rev: 12994496b6b636d75564e5ae7e938b65bca526df
GitHub-Pull-Request: golang/go#34017
Reviewed-on: https://go-review.googlesource.com/c/go/+/192877Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

Fixes #33385

Change-Id: I497ccd868d408a9c5648c72aa5ce41221368daf4
GitHub-Last-Rev: 3bf483808e10a13c522df02c2fc55fe278044680
GitHub-Pull-Request: golang/go#33423
Reviewed-on: https://go-review.googlesource.com/c/go/+/188677Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>

scanEnd is delayed one byte so we decrement
the scanner bytes count by 1 to ensure that
this value is correct in the next call of Decode.

Fixes #32399

Change-Id: I8c8698e7f95bbcf0373aceaa05319819eae9d86f
GitHub-Last-Rev: 0ac25d8de23d38c7ac577faddc6983571023f561
GitHub-Pull-Request: golang/go#32598
Reviewed-on: https://go-review.googlesource.com/c/go/+/182117Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>

The URL port is already checked in net/url, so we can remove the redundant validation in net/http.

Fixes #33600

Change-Id: I62511a452df6262d4b66180933758d34627ff9df
GitHub-Last-Rev: c19afa31025fee68ba0601bb75e9e20e09a36822
GitHub-Pull-Request: golang/go#33611
Reviewed-on: https://go-review.googlesource.com/c/go/+/190057
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

CL 187979 added set .dynsym info field, but it won't when
there are no global symbols. This CL sets that field
unconditionally.

Fixes #34000

Change-Id: Icc2f8bc74afdade88a377793e6760912b03686ba
Reviewed-on: https://go-review.googlesource.com/c/go/+/192600
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

This partly reverts CL 173417 as it incorrectly documented that Compact
performed HTML escaping and the output was safe to embed inside HTML
<script> tags. This has never been true.

Although Compact does escape U+2028 and U+2029, it doesn't escape <, >
or &. Compact is thus only performing a subset of HTML escaping and it's
output is not safe to embed inside HTML <script> tags.

A more complete fix would be for Compact to either never perform any
HTML escaping, as it was prior to CL 10883045, or to actually perform
the same HTML escaping as HTMLEscape. Neither change is likely safe
enough for go1.13.

Updates #30357

Change-Id: I912f0fe9611097d988048b28228c4a5b985080ba
GitHub-Last-Rev: aebababc9233c5705785b225377e80096d4bb8c4
GitHub-Pull-Request: golang/go#33427
Reviewed-on: https://go-review.googlesource.com/c/go/+/188717Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>

This change adds a a check in the encodeWithString.resolve method
to ensure that a reflect.Value with kind Ptr is not nil before
the type assertion to TextMarshaler.

If the value is nil, the method returns a nil error, and the map key
encodes to an empty string.

Fixes #33675

Change-Id: I0a04cf690ae67006f6a9c5f8cbb4cc99d236bca8
GitHub-Last-Rev: 6c987c90846f854e21814dbfb3a073605ec8a94c
GitHub-Pull-Request: golang/go#33700
Reviewed-on: https://go-review.googlesource.com/c/go/+/190697
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

Change-Id: I17148bb2b8021ed305ed0d230675d51c41736a11
GitHub-Last-Rev: 2998d46d10587a850fb36f5784df23b371244479
GitHub-Pull-Request: golang/go#34004
Reviewed-on: https://go-review.googlesource.com/c/go/+/192797Reviewed-by: Ingo Oeser <nightlyone@googlemail.com>
Reviewed-by: Andrew Bonventre <andybons@golang.org>

For performance reasons (avoiding costly cross-compilations) CL 177577
changed the codegen test harness to only run the tests for the
machine's GOARCH by default.

This change updates the codegen README accordingly, explaining what
all.bash does run by default and how to perform the tests for all
architectures.

Fixes #33924

Change-Id: I43328d878c3e449ebfda46f7e69963a44a511d40
Reviewed-on: https://go-review.googlesource.com/c/go/+/192619Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

Just the low-hanging fruit; code that was either never used, or its last
use was removed a while ago.

Change-Id: Ic7f90aeee3e6daf7edc16cde3c0a767d67e617ee
Reviewed-on: https://go-review.googlesource.com/c/go/+/192618
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

application/javascript is being deprecated per
https://datatracker.ietf.org/doc/draft-ietf-dispatch-javascript-mjs/

Specify a charset to be consistent with other text/* mime types.

Fixes #32351

Change-Id: I7300f6cfdbcf574103764991cb75172a252a3400
Reviewed-on: https://go-review.googlesource.com/c/go/+/186927
Run-TryBot: Andrew Bonventre <andybons@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

At the moment the last output line of ExampleSplit- two empty strings- are being
trimmed from the output.  I have formatted the output of the function to avoid
whitespace trimming and show empty strings more clearly.

Fixes #23542

Change-Id: Ic2a4d98cfa06db1466c6c6d98099542df9e7c88b
Reviewed-on: https://go-review.googlesource.com/c/go/+/191397
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

*os.File already does it.

Fixes #33064

Change-Id: I3edf0a31bf6d6e5023f47f01ebc92ed057357278
GitHub-Last-Rev: e6a5ba45d7e74def668adf145f46387ef27f5d28
GitHub-Pull-Request: golang/go#33065
Reviewed-on: https://go-review.googlesource.com/c/go/+/185857Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

This CL removes an outdated comment regarding converting a pointer to `uintptr`.
The comment was introduced in Go 1.4 and runtime GC was under the consideration of major revisions. According to the current situation, Go runtime memory allocator has no fragmentation issue. Therefore compact GC won't be implemented in the near future.

Change-Id: I5c336d81d810cf57b76797f05428421bb39a5b9f
GitHub-Last-Rev: 2ab4be3885d3f48abbcb59af3f74bc95501ff23f
GitHub-Pull-Request: golang/go#33685
Reviewed-on: https://go-review.googlesource.com/c/go/+/190520Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

wasm has 32-bit versions of all integer operations. This change
lowers RotateLeft32 to i32.rotl on wasm and intrinsifies the math/bits
call.  Benchmarking on amd64 under node.js this is ~25% faster.

node v10.15.3/amd64
name          old time/op  new time/op  delta
RotateLeft    8.37ns ± 1%  8.28ns ± 0%   -1.05%  (p=0.029 n=4+4)
RotateLeft8   11.9ns ± 1%  11.8ns ± 0%     ~     (p=0.167 n=5+5)
RotateLeft16  11.8ns ± 0%  11.8ns ± 0%     ~     (all equal)
RotateLeft32  11.9ns ± 1%   8.7ns ± 0%  -26.32%  (p=0.008 n=5+5)
RotateLeft64  8.31ns ± 1%  8.43ns ± 2%     ~     (p=0.063 n=5+5)

Updates #31265

Change-Id: I5b8e155978faeea536c4f6427ac9564d2f096a46
Reviewed-on: https://go-review.googlesource.com/c/go/+/182359
Run-TryBot: Brian Kessler <brian.m.kessler@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Richard Musiol <neelance@gmail.com>

.dynsym section info field is the index of first non-local symbol, mean
the number of local symbols.

The go linker have never ever set it before, so just set it.

Fixes #33358

Change-Id: Ifde2deb7c15471b04d565861f5d81daffb0c0d3d
Reviewed-on: https://go-review.googlesource.com/c/go/+/187979
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Previously users who opted into cgo might have received a bit of a
behavior surprise when their mingw installation defaulted to a
potentially older and different set of compatibility hacks. Since Go is
explicitly targeting >=6.1 for internal linkage, propagate these changes
to external linkage too.

While we're at it, we move these values into constant variables so that
they don't become out of sync and allow for easy updating as Go
gradually drops compatibility for older operating systems.

Change-Id: I41e654d135be6e3db9088e73efeb414933e36caa
Reviewed-on: https://go-review.googlesource.com/c/go/+/191842Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

This has been the default in MSVC for a very long time, and it's hard to
imagine modern programs actually wanting the old legacy behavior. For
example, no modern programs try to install their junk into C:\windows
and therefore need to have an emulated writable windows directory.
That's not really even allowed by ACLs on modern systems.

Change-Id: Iadaca6815e39ea5c6b05c1cac5a95cfc35e5b48a
Reviewed-on: https://go-review.googlesource.com/c/go/+/191840
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>