I'm currently porting python to some 
platforms with limited capabilities and so I thought it would be a good idea 
to subscribe here.
While doing the porting, I found two small problems in Python 2.5.1:

If Py_USING_UNICODE is disabled, in Python/ast.c decode_unicode() still calls 
unicode-related functions, which leads to undefined references when linking.

If HAVE_DYNAMIC_LOADING is disabled, in Python/import.c 
_PyImport_DynLoadFiletab is still initialized, which also leads to undefined 
references when linking, since then no source file which defines this 
variable is used.