Turn FUNCTION_ARG_OFFSET into a hook

Turn FUNCTION_ARG_OFFSET into a hook

2017-09-13  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* target.def (function_arg_offset): New hook.
	* targhooks.h (default_function_arg_offset): Declare.
	* targhooks.c (default_function_arg_offset): New function.
	* function.c (locate_and_pad_parm): Use
	targetm.calls.function_arg_offset instead of FUNCTION_ARG_OFFSET.
	* doc/tm.texi.in (FUNCTION_ARG_OFFSET): Replace with...
	(TARGET_FUNCTION_ARG_OFFSET): ...this.
	* doc/tm.texi: Regenerate.
	* config/spu/spu.h (FUNCTION_ARG_OFFSET): Delete.
	* config/spu/spu.c (spu_function_arg_offset): New function.
	(TARGET_FUNCTION_ARG_OFFSET): Redefine.
	* system.h (FUNCTION_ARG_OFFSET): Poison.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r252821