Concerning my first comment,
here is the solution to be able to us again the gnat compiler tool chain :
sudo ln -s /usr/lib/gcc/i486-linux-gnu/4.3 /usr/lib/gcc/i486-linux-gnu/4.3.1
strace tell us that the gnat command try to open /usr/lib/gcc/i486-linux-gnu/4.3.1/adainclude/system.ads, and crash as this file does not exist.
A symlink to /usr/lib/gcc/i486-linux-gnu/4.3 solve the problem ....
Concerning my first comment,
here is the solution to be able to us again the gnat compiler tool chain :
sudo ln -s /usr/lib/ gcc/i486- linux-gnu/ 4.3 /usr/lib/ gcc/i486- linux-gnu/ 4.3.1
strace tell us that the gnat command try to open /usr/lib/ gcc/i486- linux-gnu/ 4.3.1/adainclud e/system. ads,
and crash as this file does not exist.
A symlink to /usr/lib/ gcc/i486- linux-gnu/ 4.3 solve the problem ....