cmd/go: rewrite cgo names to "C." in compiler error messages
We used to do this but it broke in Go 1.10. This restores the rewrite,
but only applied to compiler output for packages that use cgo.
That is all that the original rewrite applied to anyhow.
Fixes #76339
Change-Id: Ife8ee858ddd0ff7bcc7423455b2eabf8381b7bde
Reviewed-on: https://go-review.googlesource.com/c/go/+/721821 Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org> Reviewed-by: Roland Shoemaker <roland@golang.org>