Switch to macro for STOREBGRA etc on Posix SSSE3 BUG=393 TESTED=try bots R=harryjin@google.com
Switch to macro for STOREBGRA etc on Posix SSSE3
BUG=393
TESTED=try bots
R=harryjin@google.com

Review URL: https://webrtc-codereview.appspot.com/33339004
flykickbird/libyuv,flykickbird/libyuv,flykickbird/libyuv