Patch for libstdc++-v3 cross build on hpux (Resubmit^2)

[Benjamin Kosnik]

> Steve, let me clean this file up, sanity-check my changes with other
> people, and then I'll apply an updated version of your patch.  (And
> notify you of the changed version.)  The cross-compile section of
> configure.in has quadrupled in size (not a bad thing in itself, it
> means more people are using it) since the last time I paid attention
> to it, and I'm getting confused.

Thanks for looking at this PHil.

That host-x-host part intially went in as a complete hack. Perhaps it's
time to re-think it entirely, since it seems to be used by many people
now. If there's a better way to organize this code, then feel free to do
major surgery.

-benjamin