Since some ASTs are now disabled on certain conditions, this change lets
the fuzzer know when it has generated invalid translator options.

Bug: chromium:1164448
Change-Id: I1f1b120c33fb70f9776df858db033ec914d7ad89
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2618203Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>