A no-longer-used variable controlling whether the X11 VidMode extension should be used.
Defined in SDL_hints.h
#define SDL_HINT_VIDEO_X11_XVIDMODE "SDL_VIDEO_X11_XVIDMODE"
Before SDL 2.0.24, this would let apps and users disable XVidMode support on X11. Now SDL never uses XVidMode, and does not check for this hint at all. The preprocessor define is left here for source compatibility.