Fix teststr segfault when built with -ftrivial-auto-var-init

* test/teststr.c -- one test case was broken and worked by accident: the
apr_strtok() function was intentionally called with `str == NULL` on
first invocation. This leads to an access to `*internal_state`, which is
technically undefined (uninitialized pointer on the stack).

Without `-ftrivial-auto-var-init`, the `*internal_state` is benign by
accident: the previous test case left the pointer-on-stack with some
reasonable address. However, with `-ftrivial-auto-var-init=zero`, the
`*internal_state` access fails because `internal_state = NULL`
(auto-initialized to zero). So the whole test segfaults.

This commit comments out this broken test case and also adds a new CI
workflow to cover this `-ftrivial-auto-var-init` compilation mode.

Author: dimakuv

.github/workflows/linux.yml

@@ -87,6 +87,9 @@ jobs:
             notest-cflags: -Werror
             config: --enable-maintainer-mode --with-berkeley-db --with-dbm=db5
             config-output: APU_HAVE_DB
+          - name: Auto-var-init
+            os: ubuntu-latest  # requires gcc 12 or higher
+            notest-cflags: -ftrivial-auto-var-init=zero
       fail-fast: false
 
     runs-on: ${{ matrix.os }}

test/teststr.c

@@ -48,10 +48,15 @@ static void test_strtok(abts_case *tc, void *data)
             "      asdf jkl; 77889909            \r\n\1\2\3Z",
             " \r\n\3\2\1"
         },
+#if 0
+/* don't do this... apr_strtok() is not supposed to be called with
+ * str == NULL in the first invocation, otherwise it segfaults.
+ */
         {
-            NULL,  /* but who cares if apr_strtok() segfaults? */
+            NULL,
             " \t"
         },
+#endif
 #if 0     /* don't do this... you deserve to segfault */
         {
             "a b c              ",