cmd/go: add errors obtaining c compiler version to cache key
If there's an error getting the version of the c compiler, add the error
to the input used to produce the cache key. In the case where we can't
parse the version, the text of the output of the command is part of the
error, so different unparseable versions will produce different cache
keys. Before, we wouldn't add anything to the key when there was an
error getting the version, so we wouldn't distinguish a missing compiler
from one where we couldn't parse the version.
Fixes #64589
Change-Id: I27f853e8ff40002e2f045b2210633b38f93d0130
Reviewed-on: https://go-review.googlesource.com/c/go/+/648196
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Sam Thanawalla <samthanawalla@google.com> Reviewed-by: Alan Donovan <adonovan@google.com>