If you want to test, in /osd/sdl/drawogl.c, change:
#ifndef OSD_WINDOWS
SDL_GL_SetSwapInterval(video_config.waitvsync ? 1 : 0);
#endif
by
#ifndef OSD_WINDOWS
SDL_GL_SetSwapInterval((video_config.waitvsync && fd == 0) ? 1 : 0);
#endif
Then, just in case the change above didn't work, in /osd/sdl/window.c, also change:
SDL_GL_SetAttribute(SDL_GL_SWAP_CONTROL, (video_config.waitvsync && fd == 0) ? 1 : 0);
by
SDL_GL_SetAttribute(SDL_GL_SWAP_CONTROL, 0);
That's because I'm not sure if fd is already defined at the time SDL_GL_SetAttribute is called. In previous versions both calls were inside drawogl.c and it was clearer.