GCC 15 defaults to C23, which is stricter in mutiple ways. Some fixes were
already included in 6.0.1, but some were just merged upstream and not yet
released.
The original source tarball has something out of sync, which triggers calls
to aclocal/automake after running configure. Since it was generated with
automake 1.16, it expects that exact version, and fails now in F42+ with 1.17.
Running autoreconf to force a regeneration avoids this.