cmd/go: accept clang versions with vendor prefixes
To better diagnose bugs like this one in the future, I think
we should also refuse to use a C compiler if we can't identify
a sensible version for it. I did not do that in this CL because
I want it to be small and low-risk for possible backporting.
Fixes #64423.
Change-Id: I21e44fc55f6fcf76633e4fecf6400c226a742351
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest,gotip-windows-amd64-longtest
Reviewed-on: https://go-review.googlesource.com/c/go/+/547998
Auto-Submit: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Michael Matloob <matloob@golang.org>