fortran/mpif-h: fix MPI_Alltoallw() binding

[ggouaillardet]

• ignore sendcounts, sendispls and sendtypes arguments when MPI_IN_PLACE is used
• use the right size when an inter-communicator is used.

Thanks Markus Geimer for reporting this.

Refs. #5459

Signed-off-by: Gilles Gouaillardet [email protected]

[jsquyres]

@ggouaillardet Does this need to get cherry picked to release branches?

[ggouaillardet]

@jsquyres yes, this has to be backported to the release branches.

• good news is this can be seen as a corner case
• bad news is the reported issue is the top of the iceberg. mpif-h bindings do not ignore parameters that should be ignored. Also, non blocking collectives use an intermediate malloc'ed array that is free'd right after the PMPI subroutine returns, which is incorrect since it can only be free'd after the non blocking operation completes (or is free'd if this is a persistent non blocking collective).

I am working on a patch that keeps growing, and I'd rather backport the fixes all at once.