architecture-independent GNAT project files?

["Björn Persson" <bjorn@xn--rombobjrn-67a.se>]

When I write GNAT project files for shared libraries I find that I have to
hardcode the paths to some architecture-specific directories. 32-bit
libraries are in /usr/lib/ while 64-bit libraries are in /usr/lib64/, and I
would like to have a single project file that works for both cases.

The way to find out the architecture of a Unix-like system appears to be to
invoke uname, but GNAT project files don't seem to have a shell-out
feature. As far as I can see in the manual the only ways they can get input
is by environment variables and command line parameters. I don't suppose
Gnatmake provides some variable to project files that shows what the
architecture is?

I could define an environment variable in the systemwide profile, but that's
not really a good solution. That variable would contain the host
architecture but it's the target architecture I really need to test for. I
also don't like polluting the environment.

Does anyone have a better idea?

-- 
Bj�rn Persson
PGP key A88682FD