> But doesn't removing the declaration break the build even if the function
 > isn't called?

Sure.  We can either remove x_gtk_use_window_move and call
gtk_window_move unconditionally

 >> Can you build with unstable?
 >>
 >
 > Haven't tried that (GTK appears to use a quite idiosyncratic build system),
 > but the Emacs build already breaks on Debian testing when configuring with
 > '--enable-gcc-warnings --enable-gtk-deprecation-warnings' (there are a few
 > more deprecated functions that Emacs uses).

Have these already been deprecated with GTK 3.10.8?  I'm using 3.4.2
here.  In any case please post a list of these functions here (unless
you intend to take care of them by yourself).