CMake: fix check for MPI_COMM_SHARED_TYPE using openMPI

[maelk3]

Fix CMake check for MPI_COMM_SHARED_TYPE

Following up on issue #195

Proposed changes:
This PR checks the existence of the symbol MPI_COMM_SHARED_TYPE in the header mpi.h using check_c_source_compiles instead of check_symbol_exists.

[cburstedde]

Thanks, this looks good. I can merge, but I'm also wondering whether you'd like to contribute similar code for MPITHREAD and MPIWINSHARED.

P. S. If you would please add a line to doc/release_notes.txt and add a file doc/author_lastname.txt to release under BSD?

[maelk3]

Yes, sure! Should I make another dedicaded PR or can I add to this one?

[cburstedde]

Yes, sure! Should I make another dedicaded PR or can I add to this one?

Up to you! I don't mind having this all in the same PR due to the similarity of functions to check for.

[maelk3]

@cburstedde Done!

[cburstedde]

Thanks so much, and welcome to the team! Please let us know if there's anything else that you find needs improving.

[maelk3]

Thanks!