I don’t see any platform-specific things in Vreen, by the way, instructions, too. You rather need instructions on the build environment being used.
Vreen seems to be sharpened by qbs (the build is described in Building Applications). To do this, you must have qbs installed and configured. Alternatively, you can install QtCreator (it weighs a bit, but Qt still needs to be installed), configure the compiler settings in it and build the project with qbs. Then you can already connect the library to the main project using standard methods for the development environment used.
You can try to use cmake, then you need to look for instructions on how to use qt + cmake (you need to set up environment variables correctly so that cmake finds qt and the compiler)