ubsan: Add another testcase for [0] array in the middle of struct [PR108894]

I think it is useful to cover also this, rather than just arrays at the
flexible array member positions.

2023-03-01  Jakub Jelinek  <jakub@redhat.com>

	PR sanitizer/108894
	* c-c++-common/ubsan/bounds-16.c: New test.

gcc/testsuite/c-c++-common/ubsan/bounds-16.c

+/* PR sanitizer/108894 */
+/* { dg-do run } */
+/* { dg-options "-fsanitize=bounds -fsanitize-recover=bounds" } */
+/* { dg-output "index 1 out of bounds for type 'int \\\[\[*0-9x]*\\\]'\[^\n\r]*(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*index 0 out of bounds for type 'int \\\[\[*0-9x]*\\\]'" } */
+
+struct S { int a; int b[0]; int c; } s;
+
+int
+main ()
+{
+  int *volatile p = &s.b[0];
+  p = &s.b[1];
+  int volatile q = s.b[0];
+}