Fix harmless unused parameter warnings in minimal build.

No real changes, just add some wxUnusedVar() to avoid warnings about
parameters unused in some non-default build configurations.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66090 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/bitmap.cpp

@@ -672,6 +672,8 @@ bool wxBitmap::LoadFile( const wxString &name, wxBitmapType type )
     else
 #endif
     {
+        wxUnusedVar(type); // The type is detected automatically by GDK.
+
         UnRef();
         GdkPixbuf* pixbuf = gdk_pixbuf_new_from_file(name.fn_str(), NULL);
         if (pixbuf)