Ada newbie: GNAT linking error question

[Sascha Wilde <swilde@sha-bang.de>]

I just tried to build the tetris example from

http://www.tc.umn.edu/~puk/tetris.txt

but the build fails during linking, saying:

    gnatlink tetris.ali
    b~tetris.o: In function `main':
    b~tetris.o(.text+0x489): undefined reference to `_ada_tetris'
    collect2: ld returned 1 exit status
    gnatlink: cannot call /usr/local/bin/gcc
    gnatmake: *** link failed.

Thirst I thought that might be caused by the fact that I used the gnat
compiler from gcc-3.2.3, so I tried the precompiled gnat-3.15p from
act, but it produced just the same error.  I checked it alsow on my
notebook, running debian-woody with gnat-14p the same result.
So my question is: what went wrong?

I'm not shure if this is here quite on-topic, because it might be more
a gnat than a Ada problem.  Please tell me if I'm OT here.
-- 
Sascha Wilde
    "Liebet eure Feinde, vielleicht schadet das ihrem Ruf" 
    (Stanislaw Jerzy Lec)