> Attached is a patch which basically uses fcntl if necessary to remove
> the close-on-exec flag, and tests.

Python adds extra output at the end of stderr when compiled in debug
mode. Therefore you first have to strip that output, like this:

            out, err = subprocess.Popen(...).communicate()
            err = support.strip_python_stderr(err)
            self.assertEqual((out, err), (b'apple', b'orange'))

Otherwise, looks good, thank you.