The darwin build was failing because neither of the ch4backend libraries
build on darwin.
Changes:
* delete unused argument device
* pass the derivation for the ch4backend in directly rather than using
a string to switch between two other arguments. (3 args to 1 arg)
* don't use ch4backend on Darwin
Resolves#121978
* mpich2 -> mpich
* remove slurm dependency
* use most recent gfortran
* turn enableParallelBulding on
* ensure mpi[cc,cxx,fort] uses default compilers it was built with