message: remove_unreachable_bbs:. dont crash with empty BBs
diff: @@ -1105,7 +1105,7 @@ static void remove_unreachable_bbs(Function &f) {
  do {
  auto bb = wl.back();
  wl.pop_back();
  - if (!reachable.emplace(bb).second)
  + if (!reachable.emplace(bb).second || bb->empty())
  continue;
  if (auto instr = dynamic_cast<JumpInstr*>(&bb->back())) {
  