Check whether MPI has been found before configuring it
Check whether MPI has been found before configuring it

rdebroiz/dtk,NicolasSchnitzler/dtk,rdebroiz/dtk,NicolasSchnitzler/dtk,NicolasSchnitzler/dtk,d-tk/dtk,rdebroiz/dtk,d-tk/dtk,rdebroiz/dtk,d-tk/dtk,NicolasSchnitzler/dtk,d-tk/dtk,d-tk/dtk,d-tk/dtk