Pass neon option to assembler but not the compiler.   Step 1 of unifying the two libraries back into one.
BUG=371
TESTED=local ios builds ignore the option, but still work.
R=brucedawson@google.com, harryjin@google.com

Review URL: https://webrtc-codereview.appspot.com/31719004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1145 16f28f9a-4ce2-e073-06de-1de4eb20be90