Fix bug in YUV to RGB for gcc/clang and enable affected functions.
BUG=393
TESTED=sde -ast -hsw -- out\release\libyuv_unittest.exe --gtest_catch_exceptions=0 --gtest_filter=*I422ToARGB*

Review URL: https://webrtc-codereview.appspot.com/48019004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1364 16f28f9a-4ce2-e073-06de-1de4eb20be90