GN: Fix CrOS build due to buggy "defines". This config is unfortunately not covered on the ANGLE CQ. Test: local GN CrOS build Bug: angleproject:3943 Bug: chromium:1129075 Change-Id: Ie1a9b2fdfb47f2a4631e118ab88eccfb7ad7eaf8 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2415186 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>