message: initialize the TBB
diff: #include <vector>
  #include <memory>
  +#include <stan/math/prim/core/init_threadpool_tbb.hpp>
  +
  #ifdef STAN_MPI
  #include <stan/math/prim/arr/functor/mpi_cluster.hpp>
  #include <stan/math/prim/arr/functor/mpi_command.hpp>
  @@ -104,6 +106,8 @@ namespace cmdstan {
  if (cluster.rank_ != 0) return 0;
  #endif
  + stan::math::init_threadpool_tbb();
  +
  // Read arguments
  std::vector<argument*> valid_arguments;
  valid_arguments.push_back(new arg_id());
  