Bug 767563 - Add a clang static checker, part 1: add the plugin shell. r=glandium
Bug 767563 - Add a clang static checker, part 2: Implement the MOZ_MUST_OVERRIDE attribute. r=ehsan
Bug 767563 - Add a clang static checker, part 3: Move the MOZ_MUST_OVERRIDE macro to MFBT. r=Waldo