The problem is that the warnings module's init function does not adhere
to the standard Python naming scheme for extension modules: it's called
_PyWarnings_Init rather than init_warnings. This C helper module was
added to Python 2.6.

OTOH, warnings is a builtin module which always gets imported, so the
import mechanism bypasses the normal scan for such functions.

In order to get freeze to work, it should be enough to add '_warnings'
to the list never in makeconfig.py of the freeze tool.