Debian Sarge: problem with libgnat.so

I've written a shared-lib in Ada with an additional C-interface some
years ago. Included is a little programm in C to test the interface.
Since I've updated from Debian Woody to Sarge, this C-program doesn't
compile anymore (I use Gnat-3.15p now, before it was 3.14p). Only the
C-program is affected, Ada-programs compile fine and can use the lib
without problems.

The relevant part of the Makefile is:

INCLUDE_DIR = /usr/local/include/opensteuer

.PHONY: test_c
test_c:
gcc -Wall -o test_c test_c.c -I$(INCLUDE_DIR) -lopensteuer -lgnat

And the error-message is:

gcc -Wall -o test_c test_c.c -I/usr/local/include/opensteuer -lopensteuer -lgnat
/usr/bin/ld: cannot find -lgnat
collect2: ld returned 1 exit status

The main difference between Woody and Sarge is IMHO that the link
libgnat.so in /usr/lib is missing now.

There is a link usr/lib/gcc-lib/i486-linux/2.8.1/adalib/libgnat.so
pointing to /usr/lib/libgnat-3.15p.so.1.12 but it seems not to be
found. I've added this path to /etc/ld.so.conf and to the
ADA_INCLUDE_PATH, but this makes no change.

So, I've just created this link in /usr/lib and now the compilation
works as fine as before.

What does this mean now? Is Debian Sarge misconfigurated, or is my
system misconfigurated, or is my code in the Makefile wrong?

Thanks for your help,
Martin
.