This avoids dumping -Wall warnings when they appear in framework
headers. As a result, we are closer to how regular headers are
included (via -isystem).

Also remove ccIncludeFlag lookup, this was unused & not very useful.

Bug in tests. See pytest-dev/pytest#3460

Some tests fail according to PyPy docs: http://doc.pypy.org/en/latest/faq.html#should-i-install-numpy-or-numpypy

CoreFoundation is included by the stdenv, moving the decision of what
version should be used there makes it possible to override it entirely
rather then prepending flags like cf-private does which can be
unreliable.

The only remaining use-case for cf-private are symbols that are not
available in the opensource build.  This generally solved the problem
because of it's setup-hook.

Update distutils patch to the upstream changes.
See: python/cpython@6c0e0d1

Hydra nixpkgs: ?compare=1530372

The archive that was used turned out to be incorrect.
yaml/pyyaml#320

By now a correct tarball has been uploaded but in order
to prevent issues like these we fetch now instead from GitHub.