Fix building on x86 OpenBSD 4.3

[Mark Kettenis]

> From: Pedro Alves <pedro@codesourcery.com>
> Date: Wed, 6 Aug 2008 16:10:44 +0100
> 
> Hi,
> 
> In my testing on several targets, I noticed that GDB isn't
> building on x86 OpenBSD 4.3, due to the fact that struct
> switchframe got its sf_ppl member removed, and GDB is trying
> to access it.
> 
> I can't claim I know a think about this, but,
> 
> The patch that seems to have removed it, shows that is was always
> 0 just before removal:
> 
>  http://archive.netbsd.se/?ml=openbsd-tech&a=2007-09&m=5239543
> 
> And I can see it being set to != 0 in that files' history at:
>  http://opengrok.creo.hu/openbsd/history/src/sys/arch/i386/i386/vm_machdep.c
> 
> So, I guess that the attached is the best to do, and I didn't
> notice any breakage.  Of course, I don't even know what
> triggers this code path.  :-)
> 
> Mark, perhaps you have a better fix in your local trees?

Oops, yes I have.  Fixed this and never seemed to have committed the
fix when OpenBSD 4.3 was officially released.  Need to tweak it such
that the file compiles on older OpenBSD releases though.  I guess
that's what kept me from committing this.

Thanks for pointing this out, I'll fix it ASAP.

Mark