These defines are necessary for config filtering.

BUG=angleproject:1660

Change-Id: I5bc32d8127023a0de32af75101eda13c5cdf849e
Reviewed-on: https://chromium-review.googlesource.com/425090Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>