Set MPI_DIR variable on cray systems by default, as there is no explicit module to load.

sit

@@ -77,6 +77,7 @@ else
                     module swap $COMPILER $COMPILER/$COMPILER_VERSION
                 fi
             fi
+            MPI_DIR=$MPICH_DIR
             ;;
         laki|*)
             if [ -z "$COMPILER_VERSION" ] ; then