fortran: Fix: MPI_UNWEIGHTED and MPI_WEIGHTS_EMPTY should be arrays.

Without this modification, gfortran throw the following error
if these variables are used for `MPI_DIST_GRAPH_CREATE_ADJACENT` or
`MPI_DIST_GRAPH_CREATE_ADJACENT`.

  Error: There is no specific subroutine for the generic
  'mpi_dist_graph_create_adjacent' at (1)

ompi/include/mpif-sentinels.h

@@ -53,8 +53,10 @@
       integer MPI_STATUS_IGNORE(MPI_STATUS_SIZE)
 !     Ditto for MPI_STATUSES_IGNORE
       integer MPI_STATUSES_IGNORE(MPI_STATUS_SIZE, 1)
-      integer MPI_UNWEIGHTED
-      integer MPI_WEIGHTS_EMPTY
+!     Ditto for MPI_UNWEIGHTED
+      integer MPI_UNWEIGHTED(1)
+!     Ditto for MPI_WEIGHTS_EMPTY
+      integer MPI_WEIGHTS_EMPTY(1)
 
       common/mpi_fortran_bottom/MPI_BOTTOM
       common/mpi_fortran_in_place/MPI_IN_PLACE

ompi/mpi/fortran/base/gen-mpi-mangling.pl

@@ -62,13 +62,13 @@ $fortran->{in_place} = {
     f_name => "MPI_IN_PLACE",
 };
 $fortran->{unweighted} = {
-    c_type => "int",
+    c_type => "int *",
     c_name => "mpi_fortran_unweighted",
     f_type => "integer",
     f_name => "MPI_UNWEIGHTED",
 };
 $fortran->{weights_empty} = {
-    c_type => "int",
+    c_type => "int *",
     c_name => "mpi_fortran_weights_empty",
     f_type => "integer",
     f_name => "MPI_WEIGHTS_EMPTY",