fix 2 bugs:
 - build bug libyuv.gyp
 - runtime bug in ScaleRowDown38_2_Box_NEON
BUG=
TESTED=libyuv_unittest
R=fbarchard@google.com, fbarchard@chromium.org

Review URL: https://webrtc-codereview.appspot.com/23939004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1117 16f28f9a-4ce2-e073-06de-1de4eb20be90