Fix Android ARM Neon build.

Add the GN file copied over from the clankium repository.
Fix an issue with assembly-defined functions visibility.

BUG=4183
R=andrew@webrtc.org, rtoy@google.com

Review URL: https://webrtc-codereview.appspot.com/35729004

git-svn-id: http://webrtc.googlecode.com/svn/deps/third_party/openmax@8111 4adac7df-926f-26a2-2b94-8c16560cd09d