[NDS32] Have sibling calls optmization to be performed on nds32 target.

[NDS32] Have sibling calls optmization to be performed on nds32 target.

gcc/
	* config/nds32/nds32-protos.h (nds32_expand_epilogue): Change
	prototype.
	(nds32_expand_epilogue_v3pop): Likewise.
	* config/nds32/nds32.md (sibcall): Define this for sibling call
	optimization.
	(sibcall_register): Likewise.
	(sibcall_immediate): Likewise.
	(sibcall_value): Likewise.
	(sibcall_value_register): Likewise.
	(sibcall_value_immediate): Likewise.
	(sibcall_epilogue): Likewise.
	(epilogue): Pass false to indicate this is not a sibcall epilogue.
	* config/nds32/nds32.c (nds32_expand_epilogue): Consider sibcall case.
	(nds32_expand_epilogue_v3pop): Likewise.

From-SVN: r219712