> Would you like me to file a separate bug for this issue? Or apply that patch? Or something else?

OK, if I understand correctly, the problem you describe does not affect cPython because cPython's Distutils does not use get_config_vars(), only get_config_var(); but other implementation's ports of Distutils may have diverged to use get_config_vars and so the test may fail when running under those implementations using setuptools with its newly cloned version of cPython Distutils.  If that is the case, I think it's fine to backport the fix to cPython tests in the interest of minimizing differences. Since it is minor and not really user visible, if you're willing to do so, I'm OK with a PR under this bpo and I don't think a NEWS blurb is necessary.  Thanks for bringing it up.