Use distutils.debug.DEBUG instead of distutils.core.DEBUG.
Note that distutils.core.DEBUG still works if client code uses it, but
the core code avoids circular references by using distutils.debug.
diff --git a/Lib/distutils/dist.py b/Lib/distutils/dist.py
index f995d58..92cb832 100644
--- a/Lib/distutils/dist.py
+++ b/Lib/distutils/dist.py
@@ -16,7 +16,7 @@
from distutils.fancy_getopt import FancyGetopt, translate_longopt
from distutils.util import check_environ, strtobool, rfc822_escape
from distutils import log
-from distutils.core import DEBUG
+from distutils.debug import DEBUG
# Regex to define acceptable Distutils command names. This is not *quite*
# the same as a Python NAME -- I don't allow leading underscores. The fact