stdenv/darwin: integrate a new CoreFoundation

This also updates the bootstrap tool builder to LLVM 5, but not the ones
we actually use for bootstrap. I'll make that change in a subsequent commit
so as to provide traceable provenance of the bootstrap tools.

pkgs/development/interpreters/python/cpython/2.7/boot.nix

@@ -43,6 +43,15 @@ stdenv.mkDerivation rec {
       ./deterministic-build.patch
     ];
 
+  # Hack hack hack to stop shit from failing from a missing _scproxy on Darwin. Since
+  # we only use this python for bootstrappy things, it doesn't really matter if it
+  # doesn't have perfect proxy support in urllib :) this just makes it fall back on env
+  # vars instead of attempting to read the proxy configuration automatically, so not a
+  # huge loss even if for whatever reason we did want proxy support.
+  postPatch = ''
+    substituteInPlace Lib/urllib.py --replace "if sys.platform == 'darwin'" "if False"
+  '';
+
   DETERMINISTIC_BUILD = 1;
 
   preConfigure = ''