new backend: glx: use glFinish instead of glXWaitGL

The API document claims they achieve the same thing, apparently not.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/backend/gl/glx.c

@@ -437,7 +437,7 @@ static void glx_present(backend_t *base) {
 	glXSwapBuffers(gd->display, gd->target_win);
 	// XXX there should be no need to block compton will wait for render to finish
 	if (!gd->gl.is_nvidia) {
-		glXWaitGL();
+		glFinish();
 	}
 }