[gtkada] Patch: Fix and install gtkada_gl.gpr

[Emmanuel Briot]

> This patch fixes a syntax error and two undefined variables in
> gtkada_gl.gpr, and fixes the makefile to install it.

This patch no longer applies on the development version of GtkAda, where we
have switched to using gprinstall instead of more complex Makefiles to install
GtkAda. This also provides support for uninstalled GtkAda (for those of us not
using nicer rpm packages :-)

Emmanuel