Check if WARN_UNUSED_RESULT and COMPILE_ASSERT are defined.

Works around a multiple definition error from webrtc and libjingle.

Corresponds to the libjingle change here:
https://critique.corp.google.com/#review/55489575-p10

TESTED=trybots
R=wu@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/2809004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@5025 4adac7df-926f-26a2-2b94-8c16560cd09d
2 files changed