expect avx2 compiler support means one of the avx2 functions exists. BUG=none TESTED=try bots R=bcornell@google.com
expect avx2 compiler support means one of the avx2 functions exists.
BUG=none
TESTED=try bots
R=bcornell@google.com

Review URL: https://webrtc-codereview.appspot.com/22299004
flykickbird/libyuv,flykickbird/libyuv,flykickbird/libyuv