Allows us to ignore flags passed on to us by Chromium build bots
without having to explicitly disable them. (Thanks pbos!)

TESTED=webrtc ran modules_unittests with a bogus flag did not result in an
error.

R=kjellander@chromium.org
BUG=libyuv:507

Review URL: https://codereview.chromium.org/1417573002 .