math/taucs: change metis4 dependency to metis.

We don't ship metis4 due to license concerns. Use metis 5 instead as it
is reported to work fine and it passes the same tests as the previous
version.

Use the BSD/darwin memory detection code although we still don't pass
the corresponding test.

Pet portlint while here.

PR: 234141
Approved by: thierry (mentor)