Make threads architecture-independent on Linux

[Jim Kingdon]

> I will advise against it. You can take a look at gdb 4.17.0.14 to
> see how it is handled there.

Uh, OK, I've just looked at it.  The bits to make threads
arch-independent look pretty similar to my patch to me.

Perhaps you (or someone) could offer a more specific critique?
Failing more specifics, I'd advocate checking my patch in.  That's
http://sourceware.cygnus.com/ml/gdb-patches/1999-q4/msg00207.html
for those who might have lost track.

> I will make a patch for gdb 4.18 when the backlog improves.

I don't think that waiting for future patches is a good plan.  This
isn't just directed at you, HJ, it applies equally to all the Cygnus
threads changes which are in progress and/or planned.  Especially
since just about everything being discussed (backlog, floating point,
libthread_db analogue, &c) is orthogonal to making the config
arch-independent.