S/390: Add the forgotten test for r265371

The test is part of the originally posted change
(https://gcc.gnu.org/ml/gcc-patches/2018-10/msg01173.html), but was
forgotten during svn commit.

From-SVN: r265373

gcc/testsuite/gcc.target/s390/litpool-int.c

+/* Test that we do not generate useless LAs.  */
+
+/* { dg-do compile } */
+/* { dg-options "-march=z10 -O1" } */
+
+int a;
+
+void b()
+{
+  a /= 100;
+  /* { dg-final { scan-assembler-not {(?n)\n\tla\t%r\d+,.+\(%r13\)\n} } } */
+}