Fix PR97497

Fix PR97497

This works around a limitation of gcse with handling of partially
clobbered registers.  With this patch our GOT pointer register r12 is
not marked as partially clobbered anymore for the -m31 -mzarch -fpic
combination. This is correct since all the bits in r12 we actually
care about are in fact preserved.

gcc/ChangeLog:

	PR rtl-optimization/97497
	* config/s390/s390.c (s390_hard_regno_call_part_clobbered): Do not
	return true for r12 when -fpic is used.

gcc/testsuite/ChangeLog:

	* gcc.target/s390/pr97497.c: New test.