Avoid a compiler warning
Avoid a compiler warning

If there are no built-in modules, the `builtin_module` variable is not
used, and the compiler will warn about it.

Since we're already using the variable inside a macro, we can just
declare it inside the macro block and save us the trouble altogether.

GNOME/gdk-pixbuf,GNOME/gdk-pixbuf,GNOME/gdk-pixbuf,GNOME/gdk-pixbuf