Per http://www.open-mpi.org/community/lists/devel/2015/08/17775.php,
some compilers don't like it when there's a .f90 file that only
contains comments (and no actual Fortran code). So if OMPI determines
that the Fortran compiler does not support enough Fortran mojo to
support MPI_SIZEOF, generate at least one dummy Fortran subroutine
that can be compiled in an otherwise barren Fortran landscape that is
devoid of life and hope.
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