[bug#39588] gnu: Add mpich, scalapack-mpich, mumps-mpich, pt-scotch-mpich, python-mpi4py-mpich

[Maurice Brémond]

Hi Simon,

>The digression about implicit inputs was not relevant, sorry. :-)
no worry, it made me learn some guix internals that were obscure to me!

>(arguments
> `(#:configure-flags `("-DBUILD_SHARED_LIBS:BOOL=YES")
>   #:phases (modify-phases %standard-phases
>              (add-before 'check 'mpi-setup
>        ,%openmpi-setup))))

Even if it only sets variables and should be harmless here, I don't know,
would it be easy to make this openmpi-setup become a mpi-setup with
ad-hoc initialisations?

Maurice