cmd/go: force LANG=C when looking for compiler version

Tested by installing the gcc-locales package and running
    LANG=de_DE.utf8 go build hello.go
Without this change, that fails, as described at
https://gcc.gnu.org/PR84765.

Change-Id: Ie020c33c1de9200de15aad954e7730956e2618e9
Reviewed-on: https://go-review.googlesource.com/100737
Reviewed-by: Than McIntosh <thanm@google.com>
1 file changed