add rule to Makefile to run RGFW build more quickly

shell/rgfw-loop.sml

@@ -1,20 +1,20 @@
 structure RgfwLoop =
 struct
-  fun loop (counter, window) =
+  fun loop window =
     if Rgfw.shouldCloseWindow window then
       Rgfw.closeWindow window
     else
-      let val () = print ("counter = " ^ Int.toString counter ^ "\n")
-      in loop (counter + 1, window)
+      let 
+        val () = Rgfw.swapBuffers window
+      in 
+        loop window
       end
 
   fun main () =
     let
-      val () = print "15\n"
       val window = Rgfw.createWindow ("shf", 0, 0, 1920, 1080)
-      val () = print "17\n"
     in
-      loop (0, window)
+      loop window
     end
 end