update mpi.cmake to accomodate subtle variations of config query tools.
update mpi.cmake to accomodate subtle variations of config query tools.

mpicc -showme:version sometimes prints on stderr
ompi_info has changed (-v versus -V ... ; only the bare call works
uniformly...).

mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs