After installing Developer Command Line Tools for OS X, you should have basic tools like clang and git installed. After that, you can grab other required packages via Homebrew. So as in instructions on the project page:
ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
And then:
brew install cmake sdl sdl_image sdl_ttf boost glew physfs flac libsndfile libvorbis vorbis-tools gettext po4a
Gettext is installed in separate directory without adding the files to system path, so in order to get it working normally, you should call also: