new backend: glx: use glFinish/glXWaitGL if not on NVIDIA

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

src/backend/gl/glx.c

@@ -435,6 +435,10 @@ err:
 static void glx_present(backend_t *base) {
 	struct _glx_data *gd = (void *)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();
+	}
 }
 
 static int glx_buffer_age(backend_t *base) {