S/390: Fix ICE in s390_check_qrst_address ()

S/390: Fix ICE in s390_check_qrst_address ()

In r265371 (S/390: Make "b" constraint match literal pool references)
the CONSTANT_POOL_ADDRESS_P () check was moved from
s390_loadrelative_operand_p () to s390_check_qrst_address ().  However,
in the original code it was guarded by SYMBOL_REF_P (), which was not
added to the new code.

gcc/ChangeLog:

2018-10-24  Ilya Leoshkevich  <iii@linux.ibm.com>

	* config/s390/s390.c (s390_check_qrst_address): Add the missing
	SYMBOL_REF_P () check.

gcc/testsuite/ChangeLog:

2018-10-24  Ilya Leoshkevich  <iii@linux.ibm.com>

	* gcc.target/s390/20181024-1.c: New test.

From-SVN: r265458