There are a number of additional dependencies required for getting things installed on OS X. Starting with a blank slate OS X machine, this is the process it takes:
# Install Xcode Command Line Tools
# Install Homebrew
ruby -e "$(curl -fsSkL raw.github.com/mxcl/homebrew/go)"
# Some deps
brew install node spidermonkey closure-compiler yuicompressor
brew install llvm --with-clang
cd ~/Repos
git clone git://github.com/kripken/emscripten.git
I was having trouble getting brew to install Clang 3.2 until I updated brew -- the recipes were stale. after the update brew was able to install clang 3.2. Try this