Add iOS simulator support in GN.

This builds fine on my laptop, but fails to link on the bots,
so I'm leaving out a new Build bot for now.

BUG=skia:6329

Change-Id: I4b33770f13ab9dec914d090b45d9921b19ee2c9d
Reviewed-on: https://skia-review.googlesource.com/9519
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
2 files changed