argument mismatch warnings:

Since we're anyway updating SPClibs, can we rename .f90 to .F90? :)
Since we have ifdefs present, I think it makes more sense.

(Actually I'm not sure if the violations are MPI related or not. It's possible that they're self-contained in SPClibs).

Even better would be fixing standards-compliance in bsplines ;-)
But I think that would mandate use of mpi_f08, which we should definitely keep optional.

-fallow-argument-mismatch is only legal for GCC 10+

I fear this might be a problem for ORB5, but we'll fix it on the ORB5 side by packaging vis3d if it is.
(yes, I know it was long-since agreed that vis3d would be removed).