This will allow them to be seamlessly overrideen in other repos.

Bug: angleproject:5390
Change-Id: I973cae48b5683e39ea3b07898b95956511260319
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2591107Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>