This looks like something that will have to be corrected by the Octave authors:
.macports.org_release_ports_lang_gcc40/work/gcc-4.0.4/gcc/config/ rs6000/host-darwin.c: In function 'darwin_rs6000_extra_signals': /opt/local/var/macports/build/ _opt_local_var_macports_sources_rsync .macports.org_release_ports_lang_gcc40/work/gcc-4.0.4/gcc/config/ rs6000/host-darwin.c:130: warning: passing argument 1 of 'sigaltstack' from incompatible pointer type make[2]: *** [host-darwin.o] Error 1
The Leopard release involved some changes in the signal handling internals, which generate these kinds of errors. I created some patches for Erlang, SML/NJ, and so forth to deal with it but I haven't looked at Octave. It is worth checking with the main Octave site to see if they have released any updates; most likely, other Leopard users have already complained to them about this problem. Thanks, -Brent