[PowerPC] Fix eh unwind segfault

[Christoph Hellwig]

On Mon, Aug 30, 2004 at 11:30:52PM -0700, Richard Henderson wrote:
> Short of hardware for speculative loads, the only plausible option
> would have been using mincore and praying you don't hit an munmap
> race condition.  Except that linux after 2.2 has a bug in which
> anonymous pages are *not* reported as present in core.  Which 
> includes the stack, and so makes it entirely worthless for this
> particular problem.

Linux 2.2 doesn't implement mincore at all.  Up to current Linux 2.6
mincore for anonymous mappings isn't implemented.