suzerain: use Fortran linking tag

I think this is causing issues on OpenMPI 1.6.5 because the
libsuzerain-p3dfft.la libtool archive doesn't record that
I really, really want Fortran-aware MPI linked in.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44148 0bd85f0b-c151-43b9-a1e9-27231104551f