Interestingly, Homebrew is broken right now, at least for me, given that I've installed Xcode 4.2 and it didn't seem to install GCC (instead installing LLVM) while homebrew recipes seem to require GCC. (or at least homebrew is complaining about it.)
Homebrew is warning about it, but should still attempt to compile. There is also an homebrew recipe for installing GCC v 4.6 so you can always install that...
I solved this problem by uninstalling Xcode 4.2, downloading Xcode 4.1 from Apple's site <https://developer.apple.com/downloads/index.action>; and then redownloading 4.2 and updating. You'll probably need to register to download, but it's free.
