cmd/cgo, cmd/go: add cgo -ldflags option, use it in cmd/go

cmd/cgo, cmd/go: add cgo -ldflags option, use it in cmd/go

This will automatically use a response file if ldflags is long,
avoiding "argument list too long" errors with a very large CGO_LDFLAGS.

Fixes #66456

Change-Id: I5f9ee86e03b4e6d6430f7f9d8357ef37a9c22465
Reviewed-on: https://go-review.googlesource.com/c/go/+/584655
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Commit-Queue: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>