armadillo: correct dependencies

- Remove unused dependencies atlas/blas
- Add hdf5/superlu dependency (As superlu needs openblasCompat, we also use it here.)
- Add support for darwin
- Make use of OpenBLAS-LAPACK in armadillo

OpenBLAS (confusingly) contains LAPACK already by default, so we simply use OpenBLAS when searching for LAPACK.
The better solution would be for armadillo to use cmake built in FindBLAS/FindLAPACK which both would find OpenBLAS.