[gtkada] improvements to the GtkAda build system

[Arnaud Charlet]

> For the help patch:
> * aclocal.m4 (configure --help):
> Improve the help text to clarify what --enable-shared does.
> 
> > > "Build shared libraries if supported on the target and make them
> > > preselected
> > > in project files. (By default static libraries are preselected when
> > > both
> > > kinds
> > > are built.)"
> > 
> > Looks OK to me.
> 
> A new patch with that text is attached.

This patch is OK, although I'll commit a slightly different wording.

Waiting for your other patch resubmit.

Please send one email per patch, with:

changelog+patch

in each email, rather than spreading changelogs and patches in different
emails which makes it almost impossible to follow, thanks.

Arno