Currently for Windows builds, generating the frozen modules depends on first building python.exe.  One consequence of this is that we must keep all frozen module .h files in the repo (which we'd like to avoid for various reasons).

We should be able to freeze modules before building python.exe, like we already do via our Makefile.  From what I understand, this will require that a subset of the runtime be separately buildable so we can use it in _freeze_module.c and use that before actually building python.exe.

@Steve, please correct any details I got wrong here. :)