Support for direct libc calls was added in CL 446178 but the build
tags weren't quite activating it when cgo was not enabled. Adjust them
and add a new supporting file for darwin.
This should use the new direct libc calls with both CGO_ENABLED=0 and
CGO_ENABLED=1 when building for darwin.
Updates #12524
Change-Id: Ieee4b298dee13f389ed3a63c0a4a3a18c9180163
Reviewed-on: https://go-review.googlesource.com/c/go/+/448020
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com> Reviewed-by: Michael Knyszek <mknyszek@google.com> Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Dan Peterson <danp@danp.net>
Auto-Submit: Ian Lance Taylor <iant@google.com>