S/390: Fix immediate vector operands for some builtins.

S/390: Fix immediate vector operands for some builtins.

This fixes a problem with vec_add/sub_u128 builtins.  The
s390_expand_builtin backend function is supposed to convert the
operand to TImode *AND* load it into a vector register.  The current
implementation did only the conversion and gave up then.

gcc/ChangeLog:

2019-03-11  Andreas Krebbel  <krebbel@linux.ibm.com>

	* config/s390/s390.c (s390_expand_builtin): Do the copy_to_reg not
	only on the else branch.

gcc/testsuite/ChangeLog:

2019-03-11  Andreas Krebbel  <krebbel@linux.ibm.com>

	* gcc.target/s390/zvector/vec-addc-u128.c: New test.

From-SVN: r269583