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

[dimakuv]

The apr test suite has a test error (segfault) when built with -ftrivial-auto-var-init=zero:

$ ./testall -v -q
testatomic : SUCCESS
testdir : SUCCESS
...
teststr             :  Segmentation fault

Debug stack trace:

(gdb) bt
#0 apr_strtok (str=str@entry=0x0, sep=sep@entry=0x43a429 " \t", last=last@entry=0x7fffffffe2d8) at strings/apr_strtok.c:35
#1 test_strtok (tc=0x7fffffffe380, data=<optimized out>) at test/teststr.c:81

Root cause analysis:

• apr/test/teststr.c

  Line 52 in e461da5

  NULL, /* but who cares if apr_strtok() segfaults? */

• apr/test/teststr.c

  Line 81 in e461da5

  retval1 = apr_strtok(str1, cases[curtc].sep, &state);

• The apr_strtok(str, sep, internal_state) function must not be called with str == NULL in the first invocation. However the test does exactly this, and this leads to an access to *internal_state, which is technically undefined (uninitialized pointer on the stack).
• Without -ftrivial-auto-var-init=zero, 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.

Reproducer

docker run -it amazonlinux:2023 /bin/bash

dnf install -y git vim make gcc14 autoconf libtool expat-devel
export CC=gcc14-gcc
export CFLAGS="$CFLAGS -ftrivial-auto-var-init=zero"

./buildconf
./configure
make -j
make test  # fails

cd test && ./testall -v -q  # to see the failure more clearly

Note that -ftrivial-auto-var-init=zero flag was introduced in GCC v12.

Testing the fix

$ cd test && ./testall -v -q
...
testsockopt         :  SUCCESS
teststr             :  SUCCESS  # <-- works now!
teststrnatcmp       :  SUCCESS
...

[notroj]

@dimakuv could you try adding another CI workflow to cover this compilation mode?