Neon instructions detect without using NDK so it will work within Android, and on other linux arm based platforms and builds
BUG=none
TEST=none
Review URL: https://webrtc-codereview.appspot.com/358008

git-svn-id: http://libyuv.googlecode.com/svn/trunk@153 16f28f9a-4ce2-e073-06de-1de4eb20be90