cmd/compile: remove flag_largemodel

It was added in 2013 in CL 7064048.
All uses of it in the compiler disappeared with
(or possibly before) the SSA backend.
Several releases have gone by without it,
from which I conclude that it is now not needed.

Change-Id: I2095f4ac05d4d7ab998168993a7fd5d954aeee88
Reviewed-on: https://go-review.googlesource.com/40856
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/gc/go.go

@@ -201,8 +201,6 @@ var flag_race bool
 
 var flag_msan bool
 
-var flag_largemodel bool
-
 // Whether we are adding any sort of code instrumentation, such as
 // when the race detector is enabled.
 var instrumenting bool

src/cmd/compile/internal/gc/main.go

@@ -164,9 +164,6 @@ func Main(archInit func(*Arch)) {
 	mappkg.Prefix = "go.map"
 
 	Nacl = obj.GOOS == "nacl"
-	if Nacl {
-		flag_largemodel = true
-	}
 
 	flag.BoolVar(&compiling_runtime, "+", false, "compiling runtime")
 	obj.Flagcount("%", "debug non-static initializers", &Debug['%'])
@@ -215,9 +212,6 @@ func Main(archInit func(*Arch)) {
 		flag.BoolVar(&flag_shared, "shared", false, "generate code that can be linked into a shared library")
 		flag.BoolVar(&flag_dynlink, "dynlink", false, "support references to Go symbols defined in other shared libraries")
 	}
-	if thearch.LinkArch.Family == sys.AMD64 {
-		flag.BoolVar(&flag_largemodel, "largemodel", false, "generate code that assumes a large memory model")
-	}
 	flag.StringVar(&cpuprofile, "cpuprofile", "", "write cpu profile to `file`")
 	flag.StringVar(&memprofile, "memprofile", "", "write memory profile to `file`")
 	flag.Int64Var(&memprofilerate, "memprofilerate", 0, "set runtime.MemProfileRate to `rate`")