This will allow mac_angle_rel_ng and linux_angle_rel_ng to be removed.

Bug: chromium:822310
Change-Id: I259f84c195ed4cfde17a441bf13d812a477537d1
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1565053Reviewed-by: Jamie Madill <jmadill@chromium.org>