[PATCH/RFA] ARM -- Implement ATPCS return-in-memory rules

[Richard Earnshaw]

> This implements the ATPCS return-in-memory rules for the ARM target,
> as used by arm-netbsdelf.
> 
> As with my previous ARM patch, apologies for line number fuzz ... this
> patch is relative to the previous two, which are still awaiting review.
> 
> Tested on arm-elf sim, no regressions.  OK to commit?
> 
> 	* config/arm/arm.c (arm_return_in_memory): Implement ATPCS
> 	return-in-memory rules.
> 	* config/arm/arm.h (ARM_FLAG_ATPCS, TARGET_ATPCS): Define.

OK