BUG=libyuv:698
TESTED=mm libyuv_unittest within android external/libyuv builds unittests

Change-Id: I4b5fed9f5af86c8a910f73b14053ef83f38431cc
Reviewed-on: https://chromium-review.googlesource.com/478572
Commit-Queue: Frank Barchard <fbarchard@google.com>
Reviewed-by: Frank Barchard <fbarchard@google.com>