Just from the error message that you are getting I would say that the
version of libobjc that you are using does not match your version of gcc.
There are a lot of different things you could do now, the most simple
one would be to reinstall a matching version of libobjc from your
favourite repository. Or you may want to get libobjc2 from the GNUstep
SVN repository with all its new shine features :-)
Hope this helps
Fred