We should also add a compile-only target that verifies the build works
as expected.

Bug: angleproject:3117
Change-Id: Ib55969cdd0e670c123cdbe98bd0decf2204e7267
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1650789
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>