tree-ssa-structalias.c (find_func_aliases_for_builtin_call): Handle BUILT_IN_STRDUP and BUILT_IN_STRNDUP.

	* tree-ssa-structalias.c (find_func_aliases_for_builtin_call): Handle
	BUILT_IN_STRDUP and BUILT_IN_STRNDUP.
	* tree-ssa-alias.c (call_may_clobber_ref_p_1): Likewise.  Fix
	handling of BUILT_IN_STRNCAT and BUILT_IN_STRNCAT_CHK.
	(ref_maybe_used_by_call_p_1): Fix handling of BUILT_IN_STRCAT,
	BUILT_IN_STRNCAT, BUILT_IN_STRCAT_CHK and BUILT_IN_STRNCAT_CHK.

	* gcc.dg/strlenopt-21.c: New test.

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

From-SVN: r179387