s390: Add expander for uaddc/usubc optabs

s390: Add expander for uaddc/usubc optabs

gcc/ChangeLog:

	* config/s390/s390-protos.h (s390_emit_compare): Add mode
	parameter for the resulting RTX.
	* config/s390/s390.cc (s390_emit_compare): Dito.
	(s390_emit_compare_and_swap): Change.
	(s390_expand_vec_strlen): Change.
	(s390_expand_cs_hqi): Change.
	(s390_expand_split_stack_prologue): Change.
	* config/s390/s390.md (*add<mode>3_carry1_cc): Renamed to ...
	(add<mode>3_carry1_cc): this and in order to use the
	corresponding gen function, encode CC mode into pattern.
	(*sub<mode>3_borrow_cc): Renamed to ...
	(sub<mode>3_borrow_cc): this and in order to use the
	corresponding gen function, encode CC mode into pattern.
	(*add<mode>3_alc_carry1_cc): Renamed to ...
	(add<mode>3_alc_carry1_cc): this and in order to use the
	corresponding gen function, encode CC mode into pattern.
	(sub<mode>3_slb_borrow1_cc): New.
	(uaddc<mode>5): New.
	(usubc<mode>5): New.

gcc/testsuite/ChangeLog:

	* gcc.target/s390/uaddc-1.c: New test.
	* gcc.target/s390/uaddc-2.c: New test.
	* gcc.target/s390/uaddc-3.c: New test.
	* gcc.target/s390/usubc-1.c: New test.
	* gcc.target/s390/usubc-2.c: New test.
	* gcc.target/s390/usubc-3.c: New test.