Covegl test is hard to suit gtest, so just compile it without gtest
(angle_gles1_covegl_no_gtest), we can get the test result by exit code.

Bug: angleproject:2303
Change-Id: I67a930c91f23c02e72022329c712a0749e4a903c
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2126587
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>