4470 overly aggressive D integer narrowing breaks 32-bit ustack helpers

*** 474,484 ****
          int rg;
  
          if (!dt_node_is_scalar(dst))
                  return; /* not a scalar */
          if (dstsize == srcsize &&
!             ((src->dn_flags ^ dst->dn_flags) & DT_NF_SIGNED) != 0)
                  return; /* not narrowing or changing signed-ness */
          if (dstsize > srcsize && (src->dn_flags & DT_NF_SIGNED) == 0)
                  return; /* nothing to do in this case */
  
          rg = dt_regset_alloc(drp);
--- 474,484 ----
          int rg;
  
          if (!dt_node_is_scalar(dst))
                  return; /* not a scalar */
          if (dstsize == srcsize &&
!             ((src->dn_flags ^ dst->dn_flags) & DT_NF_SIGNED) == 0)
                  return; /* not narrowing or changing signed-ness */
          if (dstsize > srcsize && (src->dn_flags & DT_NF_SIGNED) == 0)
                  return; /* nothing to do in this case */
  
          rg = dt_regset_alloc(drp);