At Mac OS X, creating a dynamic library is not possible because of problems with the way libraries are being constructed in the sdf2-bundle packages. These packages don't use libtool yet, and libtool fixes some issues with library construction.
See:
http://nix.cs.uu.nl/dist/stratego/strategoxt-0.17M1pre13791/
Several solutions are suggested:
http://gcc.gnu.org/ml/gcc/2005-06/threads.html#00179
I think that for the -fno-common we need to patch the sdf2-bundle, which is not desirable: then I'd rather change everything to libtool immediately.
Most likely, the single module option can be applied in Stratego/XT.
Testing that now ...
http://gcc.gnu.org/ml/gcc/2005-06/msg00184.html