Since you use brew, I'll assume you're using osx.
I had the same problem a few weeks ago. Here's how I solved it (be advised, it's an ugly hack):
1. Download llvm from the official website (binaries or source). If you download the source compile it.
2. Put all of the files somewhere you find convenient (I use ~/.llvm)
3. Edit ghc.conf (not sure if the name is correct), to add ~/.llvm/bin/llc (in my case) and ~/.llvm/bin/llvm where required. I don't remember the path, somewhere in lib in think. It's the file that is read when running ghc --info
It should work afterwards. Note that llvm3.4 is the latest llvm but is not tested on ghc (llvm3.3 is). I use 3.4 w/o issues though.