PR c++/79653
	* parser.c (cp_parser_std_attribute_spec): Don't build the attribute
	if the alignas expression is erroneous.
	* pt.c (tsubst_attribute): If tsubst_pack_expansion fails, return
	error_mark_node.

	* g++.dg/cpp0x/alignas10.C: New test.
	* g++.dg/cpp0x/alignas9.C: New test.

From-SVN: r245657