GN: Disable unreachable code warnings in GLES 1 tests. Bug: chromium:1240679 Change-Id: Ib140cbd32386a7836acf9a4f477693b14bf3c6d1 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3100590 Reviewed-by: Yuly Novikov <ynovikov@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>