devel/dtcmp: New port: Datatype comparison library for MPI

DTCMP provides fast, scalable comparison-based operations on MPI
datatypes, including sorting and key/value reductions, built atop lwgrp.
https://github.com/llnl/dtcmp/

It is one of the dependencies for sysutils/mpifileutils.

PR: 291588
Sponsored by: UNIS Labs
Co-authored-by: Vladimir Druzenko <vvd@FreeBSD.org>