testsuite: Fix up gcc.target/s390/pr96127.c test for modern C [PR96127]

testsuite: Fix up gcc.target/s390/pr96127.c test for modern C [PR96127]

I've noticed this test regressed on s390x-linux with the addition of the
switch to modern C patchset.  Haven't tried to reproduce the ICE, but as it
was a backend ICE and FE after warning used to add such casts before (now
errors), I think this ought to keep the testcase testing what was intended
before.

2023-12-07  Jakub Jelinek  <jakub@redhat.com>

	PR target/96127
	* gcc.target/s390/pr96127.c (c1): Add casts to long int *.