[gtkada] Patch: Make DESTDIR orthogonal to prjdir.

[Emmanuel Briot]

> 
> It's not obvious to me which tools that would be. Gnatmake, GPRbuild and the 
> gnat driver all support it in the versions we have in Fedora 17, and according 
> to the GNAT User's Guide none of the other GNAT tools understand project files 
> at all unless the gnat driver reads the project files for them.

There are several tools (not just from AdaCore) that support projects, in particular through the GNATCOLL.Projects API. I am not sure they all know about this default search location (they might, I believe we are parsing the output of gnatls -v to find the location of the default search path).

Emmanuel