Testcase for pr 21173

From-SVN: r98714

gcc/testsuite/gcc.c-torture/execute/pr21173.c

+void abort (void);
+
+char q;
+void *a[2];
+
+void foo (char *p)
+{
+  int i;
+  for (i = 0; i < 2; i++)
+    a[i] += p - &q;
+}
+
+int main (void)
+{
+  int i;
+  foo (&q);
+  for (i = 0; i < 2; i ++)
+    if (a[i])
+      abort ();
+  return 0;
+}