cmd/link/internal/ld: rewrite LC_UUID for darwin external links
When building Go binaries using external linking, rewrite the LC_UUID
Macho load command to replace the content placed there by the external
linker, so as to ensure that we get reproducible builds.
Updates #64947.
Change-Id: I263a89d1a067807404febbc801d4dade33bc3288
Reviewed-on: https://go-review.googlesource.com/c/go/+/586079
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Cherry Mui <cherryyz@google.com>