llvm/clang does not support attribute optimize.  Disable the OMITFP macro for llvm. #if defined(__APPLE__) || defined(__x86_64__) || defined(__llvm__)
BUG=83
TEST=webrtc build bots
Review URL: https://webrtc-codereview.appspot.com/787007

git-svn-id: http://libyuv.googlecode.com/svn/trunk@342 16f28f9a-4ce2-e073-06de-1de4eb20be90