Fixed mfem mpi build issue. (#6254)
Fixed mfem mpi build issue. (#6254)

* Fixed mfem mpi build issue.

* Fixed a non-mpi build issue and switched to the latest official MFEM release.

mfherbst/spack,LLNL/spack,skosukhin/spack,iulian787/spack,LLNL/spack,EmreAtes/spack,mfherbst/spack,matthiasdiener/spack,matthiasdiener/spack,krafczyk/spack,tmerrick1/spack,iulian787/spack,tmerrick1/spack,LLNL/spack,EmreAtes/spack,tmerrick1/spack,matthiasdiener/spack,skosukhin/spack,skosukhin/spack,LLNL/spack,skosukhin/spack,krafczyk/spack,LLNL/spack,EmreAtes/spack,skosukhin/spack,iulian787/spack,krafczyk/spack,EmreAtes/spack,matthiasdiener/spack,mfherbst/spack,tmerrick1/spack,EmreAtes/spack,mfherbst/spack,iulian787/spack,krafczyk/spack,matthiasdiener/spack,iulian787/spack,mfherbst/spack,krafczyk/spack,tmerrick1/spack