It’s been a long while since I’ve tinkered with Haiku_x64, but decided to pick it up again on a whim.  Downloaded the buildtools, the Haiku sources, make’d and ./configure’d the buildtools and then ran jam -q haiku-image.  Shortly thereafter, ran into the exact same error I ran into years ago!  It’s still there!  If I leave off -q, it gets a lot further, but still dies (Build Failure) at the end.  I can’t believe that JAM’ing Haiku-x64 is still impossible after over a year.  Surely there must be...