Merge pull request #3401 from kawashima-fj/pr/fortran-argv-null

fortran: Fix `MPI_ARGV(S)_NULL` compilation error

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

@@ -77,13 +77,13 @@ $fortran->{weights_empty} = {
 $fortran->{argv_null} = {
     c_type => "char *",
     c_name => "mpi_fortran_argv_null",
-    f_type => "integer",
+    f_type => "character, dimension(1)",
     f_name => "MPI_ARGV_NULL",
 };
 $fortran->{argvs_null} = {
     c_type => "char *",
     c_name => "mpi_fortran_argvs_null",
-    f_type => "integer",
+    f_type => "character, dimension(1, 1)",
     f_name => "MPI_ARGVS_NULL",
 };