Hello Mario,
I followed all the documentation tutorial for compiling SFML with your project, and I always have the same mistakes with SFML. Do you plan to update SFML support with the latest and released SFML 2.5.1 ? It won't work with the android stuff like LIBGDX as the SFML Team has stopped their work seen a long time. I need SFML/Spine working because I want to work on with the R.U.B.E. editor that works fine compiled with SFML 2.5.1. Thanks.