gcc: Drop useless objc change from r260311.

Among some of the objc changes from Apple that crept into r260311,
Radar 5355344 is incomplete and is not used since we don't carry
ObjC in the base system.

The dead code seems to have caused issues in some Tinderboxes so
get rid of it altogether.

Reported by:	luigi
MFC after:	9 days
Bring back r226403, the fix for bin/161526, which was (accidentally?)
reverted in r238896.

PR:		bin/161526
Reported by:	Karli.Sjoberg slu.se
MFC after:	3 days