Enforce clang 3.4 in USES=c*11*,objc,gnustep as clang 3.3 has some bugs

Requested by:	bapt
PR:		ports/195122
Differential Revision:	https://reviews.freebsd.org/D1181
Exp-run by:	self
With hat:	portmgr


git-svn-id: svn+ssh://svn.freebsd.org/ports/head@373004 35697150-7ecd-e111-bb59-0022644237b5