- pctrie really only requires two byte alignment so that there is a single
   bit available for a flag in the pointer.  However, it felt more correct
   to enforce natural alignment of the key pointer.  Unfortunately on
   32bit architectures 64bit integers are not always naturally aligned.
   Change the assert to enforce only 32bit alignment of the 64bit key for
   now to fix the build.  A more correct fix would be to properly sort
   the struct buf fields which definitely suffer from bloat due to padding.