mpi: use pointers for array_of_statuses

[hzhou]

Pull Request Description

Apparently some compilers -- gcc-11.2 -- will differentiate between
MPI_Status array_of_statuses[]
and
MPI_Status *array_of_statuses
and warns if we pass MPI_STATUSES_IGNORE to the former.

Note: the standard uses the former form.

Fixes #5687

[skip warnings]

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[hzhou]

test:mpich/ch3/tcp ✔️

[raffenet]

Glad we can resolve this without much intrusion.

[raffenet]

Glad we can resolve this without much intrusion.

This probably needs to be picked back to 4.0.x then since users are bound to see it.

[hzhou]

Glad we can resolve this without much intrusion.

This probably needs to be picked back to 4.0.x then since users are bound to see it.

Sure.
Separately, since the prototype now differs from the standard, it is probably worth a discussion in the forum.

[raffenet]

Glad we can resolve this without much intrusion.

This probably needs to be picked back to 4.0.x then since users are bound to see it.

Sure. Separately, since the prototype now differs from the standard, it is probably worth a discussion in the forum.

Yeah, good point. In that case let me leave 4.0.x as-is until we have some more discussion. Plus we still may see the compiler behavior revert at some later release.