testsuite/s390: Silence warning in pr80725.c

This test case checks that we do not ICE but FAILs because of
-Wint-to-pointer-cast.  Silence this warning.

gcc/testsuite/ChangeLog:

	* gcc.target/s390/pr80725.c: Add -Wno-int-to-pointer-cast.

gcc/testsuite/gcc.target/s390/pr80725.c

@@ -1,7 +1,7 @@
 /* Regression test for PR/80725.  */
 
 /* { dg-do compile } */
-/* { dg-options "-O2 -march=zEC12" } */
+/* { dg-options "-O2 -march=zEC12 -Wno-int-to-pointer-cast" } */
 
 int a, e;
 const char b;