Just a quick heads up that I just committed https://github.com/open-mpi/ompi/pull/9649, which changes Open MPI's behavior around PMIX/PRRTE and external builds. Previously, the configure script for the internally packaged PMIX and PRRTE were always run. Now, if the user specifies --with-{pmix,prrte}={external,[path]}, Open MPI's configure will not run the sub-configure for the package that the user has asked to be an external dependency. This has the side-effect of breaking "make dist" in those situations. So, going forward, if you add --with-pmix=external or --with-prrte=external on master (and likely soon 5.0), you will *not* be able to successfully run "make dist" in that build tree. You can run Open MPI's configure with no pmix/prrte arguments if you need to run "make dist". Given the general split in use cases between where you'd want to link against an external PMIX/PRRTE and where you would want to build a distribution tarball, this is not anticipated to be a problem in practice.
Thanks, Brian