Description
Enhance your MPI library to support the following:
int MPI_Reduce(const void *sendbuf, void *recvbuf, int count, MPI_Datatype datatype,
MPI_Op op, int root, MPI_Comm comm);
int MPI_Op_create(MPI_User_function *user_fn, int commute, MPI_Op *op);
MPI_Reduce only has to support MPI_INT as the data type.
MPI_Reduce is only required to support MPI_SUM as its an available *built-in* op.
However, it should also provide the possibility for the user to provide a user-defined
op by creating one with MPI_Op_create. The commute argument will not be relevant
for our purposes.
