There's a readme included with the source; it's geared toward GNU/Linux and especially Ubuntu, but it should be possible to figure out how to do it; the main difference is going to be how you install the dependencies. You need cmake, make, and the libraries Minetest uses. You can get an idea of the last one by the Ubuntu command it suggests; every word after "apt-get install" is a package name. You can look in
http://www.debian.org/distrib/packages or
http://packages.ubuntu.com/ to find out what those packages are for if you can't tell by the name of the package, and figure out what you need to do to get the same dependency for OS X.