Fix unused function warning on OSX

src/video/cocoa/cocoa_wnd.mm

@@ -166,6 +166,7 @@ static void CGDataFreeCallback(void *, const void *data, size_t)
 	delete[] (const uint32 *)data;
 }
 
+#ifdef HAVE_TOUCHBAR_SUPPORT
 /**
  * Render an OTTD sprite to a Cocoa image.
  * @param sprite_id Sprite to make a NSImage from.
@@ -191,6 +192,7 @@ static NSImage *NSImageFromSprite(SpriteID sprite_id, ZoomLevel zoom)
 
 	return [ [ [ NSImage alloc ] initWithCGImage:bitmap.get() size:NSZeroSize ] autorelease ];
 }
+#endif /* HAVE_TOUCHBAR_SUPPORT */
 
 
 /**