This assumes that you have brew and git already.
# If you want all as one command:
brew install pkg-config gtk+3 libxml2 autoconf libtool automake && git clone git://git.tuxfamily.org/gitroot/gtkatlantic/gtkatlantic.git/ gtkatlantic && cd gtkatlantic && sed -i '' 's/libtool/glibtool/g' autogen.sh && ./autogen.sh && make && make install
First, install all of the things that we need to build it: