Make it pure! A squashed commit containing the following:

Add csu

Add bootstrap_cmds

Lots of Apple packages, mostly not complete builds but enough to make progress

Update cctools

Add architecture and disable Carbon stuff in python

Add a simple TargetConditionals.h

Don’t fix libtool in our final stage

libclosure’s Block.h in libSystem.

More clang wrapper stuff, and disable otool in cctools for now

Add CommonCrypto headers

libc++abi now only depends on libunwind when not on darwin

No libc++abi tests for now, I guess

Update ancient unifdef and add more xnu purifying patches

libiconv for pkgconfig on darwin

Avoid weird readlinkat detection on darwin

Assorted purification from running it inside sandbox

Resolved conflicts:
	pkgs/development/interpreters/perl/5.16/default.nix
	pkgs/development/interpreters/python/2.7/default.nix
	pkgs/os-specific/darwin/bootstrap-cmds/default.nix
	pkgs/stdenv/darwin/default.nix
	pkgs/top-level/all-packages.nix