SDL2 CMake option names

I am currently using SDL as a part of a larger project all integrated through CMake. Given the volume of options throughout the entire project, being able to reasonably group them up helps visibility greatly. In my own version of SDL I have done exactly this, but I was hoping the changes I have made would be able to make it upstream.

All I really did was add “SDL_” to each of the exposed CMake options in the project that I could find. Pretty straightforward. I don’t know how to submit this upstream, but I can submit the file (based on trunk from a couple hours ago) or a patch file upon request.