fix to use mpicxx as a c++ compiler name when impi is used
fix to use mpicxx as a c++ compiler name when impi is used

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