Python: improve determinism

[FRidh]

Issue description

• Python 3 interpreters are not build deterministic (http://hydra.nixos.org/build/44710243#tabs-buildsteps)
• Python packages are not build determinic (should be addressed by 2bcd41b)

Related issue: #2281

[FRidh]

We might do some shopping at Debian

• 2.7: https://sources.debian.net/src/python2.7/2.7.12-7/debian/patches/
• 3.4: https://sources.debian.net/src/python3.4/3.4.2-1/debian/patches/
• 3.5: https://sources.debian.net/src/python3.5/3.5.2-8/debian/patches/
• 3.6: https://sources.debian.net/src/python3.6/3.6.0~rc1-1/debian/patches/

[globin]

Hasn't this been fixed?

[FRidh]

yep, it has! At least, for most interpreters.

See #22585

[FRidh]

There's a PR to incorporate in CPython some of the modifications I made to our CPython.
python/cpython#296