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.

Submitted by: Dmitrii Kuvaiskii <dimakuv amazon.de>
GitHub: closes #71


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/trunk@1932662 13f79535-47bb-0310-9956-ffa450edef68