Add thread_annotations for clang targets.

TESTED: As expected clang bots catched a few issues which are fixed with this CL, other bots ignore the annotations and compile fine.

R=niklas.enbom@webrtc.org, phoglund@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/6209004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@5328 4adac7df-926f-26a2-2b94-8c16560cd09d
14 files changed