It was removed in https://bugs.webkit.org/show_bug.cgi?id=161419 but wasn't removed from PlatformMac.cmake.
Created attachment 287640 [details] patch
Comment on attachment 287640 [details] patch Clearing flags on attachment: 287640 Committed r205305: <http://trac.webkit.org/changeset/205305>
All reviewed patches have been landed. Closing bug.