It's a python 2.4 modutils project (C modules called by python scripts). The setup.py compilation script tells modutils how to compile (-O flags, libs, etc), but I guess python handles the actual gcc, etc calls. Couldn't figure out why the bundled mingw behaved differently than a seperate mingw installation.
But it's not a bit deal. It would be good to figure out how to make installing a seperate mingw compiler more convenient though (right now, it's a matter of matching up the ming source code links version numbers with the same binary packages on the mingw download page and extracting 7-8 of these packages to a directory).