Semi-automatic update generated by https://github.com/ryantm/nixpkgs-update tools. This update was made based on information from https://repology.org/metapackage/mpich/versions
* mpich2 -> mpich * remove slurm dependency * use most recent gfortran * turn enableParallelBulding on * ensure mpi[cc,cxx,fort] uses default compilers it was built with