Don't create an SDL Rendered if GX is disabled

[Fancy2209]

Hello,
For a project I'm working on I'm using Aurora for most things but GX Emulation, where I want to use OpenGL directly instead.
This however could cause issues by default as without GX I'd need to modify the library to pass SDL_WINDOW_OPENGL and not create an SDL Renderer so I could make my GL context manually.
Is there a chance that at least the SDL Renderer creation could be optional?

[encounter]

Sure, the no-GX path is not very well tested or thought through. Feel free to PR changes as you go