SDL: fix glew on wayland by ignore glx

glXGetProcAddress works on wayland if linking with x11.
As long as we don't use glx related funcs, it can be ignored.
The no glx error should be handled by SDL.
Glew is only used to init gl funcs.

related:
nigels-com/glew#172

SDL/SDLGLGraphicsContext.cpp

@@ -394,7 +394,9 @@ int SDLGLGraphicsContext::Init(SDL_Window *&window, int x, int y, int mode, std:
 	if (gl_extensions.IsCoreContext) {
 		glewExperimental = true;
 	}
-	if (GLEW_OK != glewInit()) {
+	GLenum glew_err = glewInit();
+	// glx is not required, igore.
+	if (glew_err != GLEW_OK && glew_err != GLEW_ERROR_NO_GLX_DISPLAY) {
 		printf("Failed to initialize glew!\n");
 		return 1;
 	}