MPI 4.1 - mpif.h is deprecated

[hppritcha]

not sure how we would like to handle this but see
MPI Forum issue mpi-forum/mpi-issues#561
item 6 in Section B1.2 of the MPI 4.1 standard

[devreal]

We could just place a preprocessor #warning in the header.

[jeffhammond]

There is no standard Fortran preprocessor and whether the non-standard variants are enabled usually depends on the file suffix (.F/F90 are preprocessed, .f/f90 are not). If you add #warning, you'll break the build in some cases.

What you could do is add a check in the compiler wrapper scripts to see if mpif.h is included and warn based on that.