Dion,
Did you configure with threads enabled? I think that may be the problem.
debian:/usr/local/src/tcl8.4.5_cvs/unix# make distclean
debian:/usr/local/src/tcl8.4.5_cvs/unix# ./configure --enable-threads
debian:/usr/local/src/tcl8.4.5_cvs/unix# make
debian:/usr/local/src/tcl8.4.5_cvs/unix# make install
/Ola