That is, when associated statements print separately, print comments
clearly delineating and associating the OpenACC and OpenMP
alternatives.

For example:

  int i;
  #pragma acc parallel
  #pragma acc loop vector
  for (i = 0; i < 4; ++i)
    ;

prints with -fopenacc-print=acc-omp as:

  int i;
  #pragma acc parallel
  // #pragma omp target teams firstprivate(i)
  // v----------ACC----------v
  #pragma acc loop vector
  for (i = 0; i < 4; ++i)
    ;
  // ---------ACC->OMP--------
  // {
  //     int i;
  //     #pragma omp parallel for simd num_threads(1)
  //         for (i = 0; i < 4; ++i)
  //             ;
  // }
  // ^----------OMP----------^