cmd/link: exit early when -d is used on libc platforms

On platforms where we use libc for syscalls, we dynamically link
with libc and therefore dynamic linking cannot be disabled. Exit
early when -d is specified.

Update #42459.

Change-Id: I05abfe111df723b5ee512ceafef734e3804dd0a8
Reviewed-on: https://go-review.googlesource.com/c/go/+/365658


Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>