J?rgen Tjern?
If you #define NO_SDL_GLEXT before including SDL_opengl.h, it still includes the platform-provided glext.h. The comments indicate that this define is intended to be used when you provide your own glext.h (quote from SDL_opengl.h: "Define this if you have your own version of glext.h and want to disable the version included in SDL_opengl.h.")
This is a problem because glext.h depends on the contents of gl.h, and it's practical to let SDL_opengl.h pick the right #include for gl.h for our platform.
