* expr.c (expand_expr_real_1) <case CALL_EXPR>: Use get_callee_fndecl

	* expr.c (expand_expr_real_1) <case CALL_EXPR>: Use get_callee_fndecl
	instead of checking CALL_EXPR_FN directly to test for builtins.
	If error or warning attributes are present, print
	error resp. warning.
	* c-common.c (handle_error_attribute): New function.
	(c_common_attribute_table): Add error and warning
	attributes.
	* doc/extend.texi: Document error and warning attributes.

	* gcc.dg/va-arg-pack-len-1.c: Use error and warning
	attributes.
	* gcc.dg/va-arg-pack-len-2.c: New test.
	* g++.dg/ext/va-arg-pack-len-1.C: Use error and warning
	attributes.
	* g++.dg/ext/va-arg-pack-len-2.C: New test.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@128687 138bc75d-0d04-0410-961f-82ee72b054a4