CRIS: Fix PR middle-end/113109; "throw" failing

CRIS: Fix PR middle-end/113109; "throw" failing

TL;DR: the "dse1" pass removed the eh-return-address store.  The
PA also marks its EH_RETURN_HANDLER_RTX as volatile, for the same
reason, as does visum.  See PR32769 - it's the same thing on PA.

Conceptually, it's logical that stores to incoming args are
optimized out on the return path or if no loads are seen -
at least before epilogue expansion, when the subsequent load
isn't seen in the RTL, as is the case for the "dse1" pass.

I haven't looked into why this problem, that appeared for the PA
already in 2007, was seen for CRIS only recently (with
r14-6674-g4759383245ac97).

	PR middle-end/113109
	* config/cris/cris.cc (cris_eh_return_handler_rtx): New function.
	* config/cris/cris-protos.h (cris_eh_return_handler_rtx): Prototype.
	* config/cris/cris.h (EH_RETURN_HANDLER_RTX): Redefine to call
	cris_eh_return_handler_rtx.