Compiling requires some prerequisites

Clone git repository of SDLAda https://github.com/Lucretia/sdlada and follow instructions as provided in README.md file.
Install SDL2-devel and SDL2_image-devel (depending on your Linux distribution the names of the packages may vary somewhat).
Update the threed.gpr file so that it contains full pathname of sdlada/share/gpr/sdlada.gpr".
gprbuild -largs $(pkg-config sdl2 SDL2_image --libs) (install additional packages as required).
If everything goes as planned you will have an executable file created which can be run from the command line.