I know that's a pretty aggressive optimization level, but that's what
it defaulted to.

Per Doug's message, I switched pjl-toolset to gcc, and the
regressions are running now. We'll see in a few hours how this turns
out, I suppose.

That Boost.Filesystem yields an ICE leaves me none-too-optimistic for this new version. I've submitted bug reports on this since Workshop 6u2.