bpo-44035: Check autoconf files thoroughly (GH-29935)

Check that users don't push changes with outdated or patched autoconf.
The presence of runstatedir option and aclocal 1.16.3 are good markers.

Use my container image to regenerate autoconf files. "Check for changes"
will fail later when any file is regenerated.

Use ccache in check_generated_files to speed up testing.