So far usage of 128 bit add/sub instruction was rejected if the second
operand was a constant because the predicate rejected this.

gcc/testsuite/ChangeLog:

	* gcc.target/s390/vector/int128-1.c: New test.

gcc/ChangeLog:

	* config/s390/vector.md ("<ti*>add<mode>3", "<ti*>sub<mode>3"):
	Change the predicate of op2 from nonimmediate to general and let
	reload fix it if necessary.

From-SVN: r233554