message: helper: add more MPI_Datatype values to mpidummy
diff: @@ -57,6 +57,7 @@ typedef int MPI_Op;
  #define MPI_COMM_WORLD 1
  #define MPI_COMM_SELF 2
  +#define MPI_DATATYPE_NULL 0
  #define MPI_INT 1
  #define MPI_CHAR 2
  #define MPI_DOUBLE 3
  @@ -74,6 +75,7 @@ typedef int MPI_Op;
  #define MPI_DOUBLE_INT 15
  #define MPI_LONG_DOUBLE_INT 16
  #define MPI_SHORT_INT 17
  +#define MPI_SIGNED_CHAR 18
  #define MPI_ANY_SOURCE 0
  #define MPI_ANY_TAG 0
  