[NDS32] Support dwarf exception handling.

[NDS32] Support dwarf exception handling.

gcc/
	* config/nds32/constants.md (unspec_volatile_element): Add
	UNSPEC_VOLATILE_EH_RETURN.
	* config/nds32/nds32-md-auxiliary.c (nds32_output_stack_push,
	nds32_output_stack_pop): Support dwarf exception handling process.
	* config/nds32/nds32-protos.h (nds32_dynamic_chain_address): Declare.
	* config/nds32/nds32.c (nds32_init_machine_status): Support dwarf
	exception handling process.
	(nds32_compute_stack_frame): Likewise.
	(nds32_return_addr_rtx): Likewise.
	(nds32_initial_elimination_offset): Likewise.
	(nds32_expand_prologue): Likewise.
	(nds32_expand_epilogue): Likewise.
	(nds32_dynamic_chain_address): New function.
	* config/nds32/nds32.h (machine_function): Add fields for dwarf
	exception handling.
	(DYNAMIC_CHAIN_ADDRESS): Define.
	(EH_RETURN_DATA_REGNO): Define.
	(EH_RETURN_STACKADJ_RTX): Define.
	* config/nds32/nds32.md (eh_return, nds32_eh_return): Implement
	patterns for dwarf exception handling.

From-SVN: r259210