message: unroll: dont attempt to delete unsused phis; preprocess can do that if needed
  + fix compilation failure with clang
diff: @@ -626,9 +626,11 @@ void Function::unroll(unsigned k) {
  phi && user_bb == dst) {
  // Check if the phi uses this value through this predecessor
  auto &vals = phi->getValues();
  + auto *used_val = val;
  + auto *ex = exit;
  if (!any_of(vals.begin(), vals.end(),
  [&](const auto &p) {
  - return p.first == val && &getBB(p.second) == exit;
  + return p.first == used_val && &getBB(p.second) == ex;
  }))
  continue;
  @@ -715,10 +717,6 @@ void Function::unroll(unsigned k) {
  i->rauw(*first_added_phi, *load.get());
  user_bb->addInstrAt(move(load), i, true);
  - for (auto &[bb, phi] : added_phis) {
  - bb->delInstr(phi);
  - }
  -
  getFirstBB().addInstr(move(alloca), true);
  }
  }
  