PR target/79890: S/390: Fix crash.

PR target/79890: S/390: Fix crash.

builtin_eh_return requires the return address to be saved on the
stack.  The patch prevents using an FPR for that.

gcc/ChangeLog:

2017-04-05  Dominik Vogt  <vogt@linux.vnet.ibm.com>

	PR target/79890
	* config/s390/s390.c (s390_register_info_gprtofpr): Return if
	call_eh_return is true.

gcc/testsuite/ChangeLog:

2017-04-05  Dominik Vogt  <vogt@linux.vnet.ibm.com>

	PR target/79890
	* gcc.target/s390/pr79890.c: New test case.

From-SVN: r246701