re PR tree-optimization/18828 (Extraneous warning with var_start and optimization)

re PR tree-optimization/18828 (Extraneous warning with var_start and optimization)

	PR tree-optimization/18828
	* builtins.c (expand_builtin_next_arg): Remove argument and all
	the argument checking.
	(expand_builtin): Adjust caller.
	(expand_builtin_va_start): Likewise.  Remove error for too many
	arguments.
	(fold_builtin_next_arg): Issue error for too many arguments.
	After checking arguments, replace them with magic arguments that
	prevent further checking of the args.

	* gcc.dg/20050105-2.c: New test.

From-SVN: r93040