This ports https://crrev.com/c/1185020
[Fuchsia] Add Mac build support.

This also rolls v8/build:
https://chromium.googlesource.com/chromium/src/build/+log/9f16b23..ed29828

TBR=yangguo@chromium.org

Bug: chromium:707030
Change-Id: Ib74df070fa4a2b77c4837f82e4e4d8666a3166e5
Reviewed-on: https://chromium-review.googlesource.com/1199404
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55555}