IBM Z: Fix long double <-> DFP conversions

IBM Z: Fix long double <-> DFP conversions

When switching the s390 backend to store long doubles in vector
registers, the patterns for long double <-> DFP conversions were
forgotten.  This did not cause observable problems so far, because
libdfp calls are emitted instead of pfpo.  However, when building
libdfp itself, this leads to infinite recursion.

gcc/ChangeLog:

	PR target/99134
	* config/s390/vector.md (trunctf<DFP_ALL:mode>2_vr): New
	pattern.
	(trunctf<DFP_ALL:mode>2): Likewise.
	(trunctdtf2_vr): Likewise.
	(trunctdtf2): Likewise.
	(extend<DFP_ALL:mode>tf2_vr): Likewise.
	(extend<DFP_ALL:mode>tf2): Likewise.
	(extendtftd2_vr): Likewise.
	(extendtftd2): Likewise.

gcc/testsuite/ChangeLog:

	PR target/99134
	* gcc.target/s390/vector/long-double-from-decimal128.c: New test.
	* gcc.target/s390/vector/long-double-from-decimal32.c: New test.
	* gcc.target/s390/vector/long-double-from-decimal64.c: New test.
	* gcc.target/s390/vector/long-double-to-decimal128.c: New test.
	* gcc.target/s390/vector/long-double-to-decimal32.c: New test.
	* gcc.target/s390/vector/long-double-to-decimal64.c: New test.