openmpi/mpich: add support for clang12, and clang13 too if possible

[mascguy (Christopher Nielsen)]

Since MacPorts Clang 12 has had time to mature, it's worth testing both openmpi and mpich to see if they'll build and function with it.

It might also be worth testing with Clang 13 as well.

[Christopher Nielsen <mascguy@…>]

In ff34b6db8b3260f664c67213cf15c188c5aae02a/macports-ports (master):

mpi pg: disable clang 13 for openmpi/mpich

• Not yet supported by our MPI-related ports

See: #63608

[mascguy (Christopher Nielsen)]

Update: Still waiting to see whether openmpi and mpich build successfully, with Clang 12 and 13. But one thing that was immediately apparent, is the need to cleanup implicit function declarations.

Hopefully it shouldn't be a big deal to fix, at least in principle. But definitely needs to be done before release, particularly for ARM.

[mascguy (Christopher Nielsen)]

Good News: openmpi and mpich both build successfully, against Clang 12 and 13. No surprise, but still great to see.

Next step is to fix the implicit function declarations.

[eborisch (Eric A. Borisch)]

See ​https://github.com/macports/macports-ports/pull/13416 for WIP port. Any reason not to push the green button?

[kencu (Ken)]

see also #64436

[mascguy (Christopher Nielsen)]

Fixed, thanks to work from Eric and others.