Reland "Fuchsia: Stop setting OS_POSIX"

This is a reland of 90f86c118d322a2ad437157a71cef8fc43a17d01

Original change's description:
> Fuchsia: Stop setting OS_POSIX
>
> Bug: 836416
> Change-Id: Ib59796358ff2109ec0b55686974a84980e18254e
> Reviewed-on: https://chromium-review.googlesource.com/1020375
> Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Reviewed-by: Scott Graham <scottmg@chromium.org>
> Reviewed-by: Matt Mueller <mattm@chromium.org>
> Reviewed-by: Victor Costan <pwnall@chromium.org>
> Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#560013}

Bug: 836416
Change-Id: I43f34aa644e51d231c7c131b4be364b6ccee2d38
Reviewed-on: https://chromium-review.googlesource.com/1066711
Reviewed-by: Victor Costan <pwnall@chromium.org>
Reviewed-by: Scott Graham <scottmg@chromium.org>
Reviewed-by: Matt Mueller <mattm@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560828}

CrOS-Libchrome-Original-Commit: 65421f69a6e0e69991c3d6521f98efa8647b547f
11 files changed
tree: 5049989dedae5791e0858f984a90a8e37a6022ac
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/