> - build postgresql (except for the tcl lib)
> - install it (including libpq.so)
> - build the postgresql tcl interface library, linking against the
>   installed libpq.so
> - install the tcl lib

I'm not clear about such a thing at all. But according to Info of LD,
'-rpath-link' option would help.

I have, similar problem linking readline library to PostgreSQL (psql),
Python, or Guile. I wonder this is called as interlibrary dependency
problem.

Well, even so, I have no clue at all. :(

Masao