Merge pull request #5779 from RosettaCommons/vmullig/fix_mpi_build_issue_on_ubuntu
Fix MPI build on newer Ubuntu
Disabling C++ MPI bindings in MPI builds. This is to correct a known issue with newer GCC building against older (e.g. v. 1.10.7) OpenMPI. This is safe to do since (a) we don't use the C++ bindings (only the C bindings), (b) the C++ bindings were redundant and useless anyways, and (c) the C++ bindings have been removed in OpenMPI 4.