Add support for copy specifiers in fnspec

	* attr-fnspec.h: Update topleve comment.
	(attr_fnspec::arg_direct_p): Accept 1...9.
	(attr_fnspec::arg_maybe_written_p): Reject 1...9.
	(attr_fnspec::arg_copied_to_arg_p): New member function.
	* builtins.c (builtin_fnspec): Update fnspec of block copy.
	* tree-ssa-alias.c (attr_fnspec::verify): Update.