cmd/link: support cgo internal/linking on darwin/arm64

cmd/link: support cgo internal/linking on darwin/arm64

Cgo programs work as well. Still not enabled by default for now.

Enable internal linking tests.

Updates #38485.

Change-Id: I8324a5c263fba221eb4e67d71207ca84fa241e6c
Reviewed-on: https://go-review.googlesource.com/c/go/+/263637
Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>