system.h (FUNCTION_ARG, [...]): Poison.

system.h (FUNCTION_ARG, [...]): Poison.

	* system.h (FUNCTION_ARG, FUNCTION_INCOMING_ARG): Poison.
	(FUNCTION_ARG_ADVANCE): Likewise.
	* tm.texi.in: Change references to them to hook references.
	* tm.texi: Regenerate.
	* targhooks.c (default_function_arg): Eliminate check for target
	macro.
	(default_function_incoming_arg): Likewise.
	(default_function_arg_advance): Likewise.
	* target.def (function_arg, function_incoming_arg): Change to
	DEFHOOK.
	(function_arg_advance): Likewise.
	* target-def.h: Eliminate FUNCTION_INCOMING_ARG check.

From-SVN: r171389