Comment test cases
*-closure may need to avoid stack shuffling elimination in certain cases

- Try to mitigate this by prefering older stack slot as destination
  for arithmetic operations (the rationale being that the older stack
  slot is the one more likely having been alive on closure entry).
  But this can break as well, so be conservative and fall back to
  straighforward translation if the stack layout changes during the
  closure body's execution.