[gtkada] improvements to the GtkAda build system

[Arnaud Charlet]

> On the other hand the relative paths don't work in a 64-bit Fedora where the
> libraries are in /usr/lib64 but the project files have to be in
> /usr/lib/gnat.

They don't "have to be", you could change that (either via a system wide env
variable, or by modifying gnat tools).

> I suppose I could make an option to allow choosing between absolute and
> relative paths. Is there a chance that you would accept that?

Not really, that would add a level of complexity that would hurt
maintenance I suspect.