re PR middle-end/45838 (FAIL: libgomp.c/pr34513.c execution test)

	PR middle-end/45838
	* tree-ssa-alias.c (ref_maybe_used_by_call_p_1,
	call_may_clobber_ref_p_1): Return true for __sync_* and some
	OpenMP builtins that act as threading barriers.

Co-Authored-By: Richard Guenther <rguenther@suse.de>

From-SVN: r166863