In msg111399 I remarked the new itertools dependency. It seems it is in fact problematic because when building Python from scratch `setup.py` which is used to build C extensions is using configparser. And one of the C-only modules is itertools :)
Attached a new patch that doesn't include itertools dependencies. The only difference with the last one is:
96d95
< import itertools
549,550c548,550
< all_sections = itertools.chain([self._defaults],
< self._sections.values())
---
> all_sections = [self._defaults]
> all_sections.extend(self._sections.values())
>