You need the PHost development kit (PDK) that is available here: <http://phost-contrib.sourceforge.net/>
If you just want it compiled, and that's it, use the enclosed Makefile. Adjust the variables at the top and type make.
If you want to seriously modify it, use the Makefile generator from <https://github.com/stefanreuther/accidental-build>. Create a build directory, and type
/path/to/Make.pl IN=/path/to/source PDK_DIR=/path/to/pdk make
This will create a Makefile suited for development, which does automatic dependencies, automatic rebuild on rule change, and out-of-tree build.
In any case, the build result will be a binary cactus that is the entire add-on.
So far, Agave Tequilana has been tested only on Linux with PHost.
