Generic reimplementations of Apple drivers for S5L and also extra build utilities to allow kernel extensions to be compiled for armv7. A hacked up SDK is required to work with this to create working kernel extensions and other binaries.
I'll eventually upload a copy of my SDK somewhere else so that people can use it. I used the OS X 10.8 SDK with the xnu-1699 source tree for generating export lists, these were used to form the System.kext plugins used to build for ARM. I don't imagine this being so hard to generate if you have a kernel for your device already.
The OS X xcspec builds for armv7 or x86_64. Very bad, I know, but it worked for building a lot of the projects from opensource.apple.com. It's amazing what can be done with the resources Apple gives you for everything.
Fixing kxld to work with ARM is relatively simple, add support for ARM binaries in the kxld_object.c file in the xnu source tree. Kextsymboltool requires an -arch armv7 parameter too. The System.kext should be fully compatible with Darwin 11 from iOS 4.3/5.0. (I think.)