[gtkada] circular dependency on gtkada rm document generation

[Emmanuel Briot]

> 1) Is there really no way RM documentation can be built *WITHOUT* GPS? (I mean could a reasonable change be made to eliminate the requirement of GPS because it's obvious it's needed right now)
> 2) Is it possible to have the RM documentation as a download?

1) no, the generation of the documentation depends on GPS currently.
2) That's what we do when we distribute GtkAda to our customers or on the libre site
    in fact. Check the directory docs/gtkada_rm/gtkada_rm