I was kindof put off by the lack of compilation instructions, but it seems the following quite obvious was enough:
g++ -c ghostscript.cpp `wx-config --cxxflags` `gtk-config --cflags`
... now i'll see how hard it is to get a libgs.so built ;).
The instructions point you to using the supplied makefiles (for gcc-based builds). They are in build-specific sub-directories.