b021e09fc0
Building it as a shared library causes issues distributing it to an AppImage, since linuxdeploy expects the executable to only dynamically link to system libraries. Additionally, simply dynamically linking to a library in the binary directory is bound to cause issues. Solution is to use SDL's CMake switches and build it statically. We also alias `SDL2` to `SDL2-static` on the external submodule for compatibility with the rest of the project.