This is a follow-up to review comments on CL 7696.

I believe that this includes the first regular Go test in the compiler.

No functional changes. Passes toolstash -cmp.

Change-Id: Id45f51aa664c5d52ece2a61cd7d8417159ce3cf0
Reviewed-on: https://go-review.googlesource.com/7820Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>