pnmpi@1.7: new package (#7051)
pnmpi@1.7: new package (#7051)

Add PnMPI, a dynamic MPI tool infrastructure that builds on top of the
PMPI interface.
iulian787/spack,mfherbst/spack,EmreAtes/spack,mfherbst/spack,tmerrick1/spack,iulian787/spack,tmerrick1/spack,LLNL/spack,LLNL/spack,EmreAtes/spack,matthiasdiener/spack,iulian787/spack,matthiasdiener/spack,krafczyk/spack,iulian787/spack,EmreAtes/spack,LLNL/spack,tmerrick1/spack,mfherbst/spack,krafczyk/spack,matthiasdiener/spack,mfherbst/spack,LLNL/spack,EmreAtes/spack,iulian787/spack,matthiasdiener/spack,LLNL/spack,krafczyk/spack,EmreAtes/spack,mfherbst/spack,krafczyk/spack,krafczyk/spack,matthiasdiener/spack,tmerrick1/spack,tmerrick1/spack