Add temporary ifdef to allows non MPI build

src/utils/Partitioner.cpp

 #include <Partitioner.hpp>
 #include <Messenger.hpp>
 
+#ifdef PASTIS_HAS_MPI
+
 #include <parmetis.h>
 #include <vector>
 
@@ -76,3 +78,9 @@ Partitioner()
   Messenger::destroy();
   std::exit(0);
 }
+
+#else // PASTIS_HAS_MPI
+
+Partitioner::Partitioner() {}
+
+#endif // PASTIS_HAS_MPI