[ANGLE] Improve compile-time macOS guards and avoid ObjC if possible
Created attachment 381740 [details] Patch
Created attachment 381742 [details] Patch
Note that there are important steps to take when updating ANGLE. See http://trac.webkit.org/wiki/UpdatingANGLE
Created attachment 381744 [details] Patch
Committed r251510: <https://trac.webkit.org/changeset/251510>
<rdar://problem/56560444>