-- How to build the HFS Kexts --

1. Install headers from XNU.  Typically, after downloading the XNU
source, you want to do something like:

$ mkdir -p BUILD.hdrs/obj BUILD.hdrs/sym BUILD.hdrs/dst

$ make installhdrs SDKROOT=macosx ARCH_CONFIGS=X86_64 SRCROOT=$PWD \
	OBJROOT=$PWD/BUILD.hdrs/obj SYMROOT=$PWD/BUILD.hdrs/sym \
	DSTROOT=$PWD/BUILD.hdrs/dst

$ sudo ditto BUILD.hdrs/dst `xcrun -sdk macosx -show-sdk-path`

2. Build the Kexts:

$ xcodebuild -target kext -target encodings-kext SDKROOT=macosx

N.B. At the time of writing, the other HFS targets are known not to
build outside of Apple's internal build environment.