In general we don't assume that the go command knows the
specific version of the compiler being used, including which
experiments the compiler was built with. Let the compiler tell us,
instead of importing cmd/internal/objabi from cmd/go.
Replacement for CL 128735.
Change-Id: Iaa07f46e19764d0fb14a1c89979bea7bb7139b9c
Reviewed-on: https://go-review.googlesource.com/c/149338 Reviewed-by: Bryan C. Mills <bcmills@google.com>