cmd/go: only attempt to match subset of $GOCACHE in test
This test attempted to be clever by looking for the entirety of $GOCACHE
in the compile command line to ensure that the profile was coming from
cache.
Unfortunately, on Windows $GOCACHE contains \, which needs extra
escaping in a regexp. As an approximate alternative, just look for the
"gocache" component specified when defining GOCACHE.
This fixes the Windows longtest builders.
Cq-Include-Trybots: luci.golang.try:gotip-windows-amd64-longtest
Change-Id: If6c77cf066d8612431e0720405254e1fdf528e9b
Reviewed-on: https://go-review.googlesource.com/c/go/+/580137 Reviewed-by: Than McIntosh <thanm@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Bypass: Michael Pratt <mpratt@google.com>