The time64 switchover I had been testing and hoped to push yesterday
turned out to be missing the ioctl and sockopt bits, which I
eventually remembered I'd omitted in the late-summer i386-only draft
because making a bunch more archs have arch variants for these did not
seem fun. So, I've worked out some changes to allow top-level socket.h
to do a lot more. The msghdr move is pretty much orthogonal, aside
from interaction with x32.

It's probably not perfect at this point, but I think it's an
improvement, and short of errors good enough to commit. It brings
things closer to a state of only needing arch-specific bits for archs
that actually do weird things, rather than repeating things that are
universal to all 32-bit archs or all 64-bit archs on a per-arch basis.

These patches should apply ok on the last time64 switchover draft
posted to the list. But I'm posting them more for the sake of a (very
brief) comment period about what they're doing, and to have a record
of them as individual patches -- some of them will be squashed since
they yield ABI-inconsistent revisions if left split.

Rich