Please don't think of these as canonical build instructions yet, as this work is rather early along. Let me tell you what's working for me, and hopefully this information will be enough to get you going.
Firstly, you'll need to have LLVM. I recommend installing LLVM version 2.8 or later (from llvm.org), which is what this package has been tested with.
It's easy to install LLVM itself from source:
cd llvm
./configure --prefix=$SOMEWHERE
make
make install
It's a good idea to have $SOMEWHERE/bin in your path.
Installing from source on Windows requires MinGW.
This is a normal Haskell package, but needs a configure script to
configure some system-specific details of LLVM.
cabal install --configure-option --with-llvm-prefix=$SOMEWHERE
If you have LLVM installed in a fairly normal location (/usr or
/usr/local), you don't need the --configure-option bits.
In the examples directory are a few example programs. There's a GNU
Makefile in there, so running make in that directory will build the
examples, as will make examples in the top-level directory. Doing
make run will build and run the examples.
Note: On older versions of MacOS X you may see a lot of "atom sorting error" warnings. They seem to be harmless.