[ARC] Introduce ADJUST_REG_ALLOC_ORDER.

[ARC] Introduce ADJUST_REG_ALLOC_ORDER.

The ARC port is changing the allocation order in the
arc_conditional_register_usage function, but this is not the proper
way. Thus, we employ ADJUST_REG_ALLOC_ORDER hook for this task.

gcc/
xxxx-xx-xx  Claudiu Zissulescu  <claziss@synopsys.com>

	* config/arc/arc-protos.h (arc_adjust_reg_alloc_order): Declare.
	* config/arc/arc.c (arc_conditional_register_usage): Remove all
	reg_alloc_order references.
	(size_alloc_order): Define.
	(arc_adjust_reg_alloc_order): New function.
	* config/arc/arc.h (REG_ALLOC_ORDER): Proper define the register
	order.
	(ADJUST_REG_ALLOC_ORDER): Define.
	(HONOR_REG_ALLOC_ORDER): Likewise.

From-SVN: r269755