Fix error messages related to undefined symbols in lwlink Make lwlink not complain about seciton base and length symbols. Also silence duplicate complaints about undefined symbols. There is no need to complain about undefined symbols during the file/section resolution stage! If they are truly undefined, they'll still be undefined at the reference resolution stage.

The lwbasic directory is an in-progress attempt to write a compiler for a
dialect of basic specifically targetted at the 6809 CPU. It is still
incomplete but is included in this distribution in case someone finds the
code useful. It is not built by default.