more cancellation work

[David Mosberger]

>>>>> On Tue, 15 Jul 2003 18:23:23 -0700, Richard Henderson <rth@twiddle.net> said:

  Richard> On Tue, Jul 15, 2003 at 04:27:00PM -0700, David Mosberger
  Richard> wrote:

  >> You do know that the ia64 unwinder in gcc is broken, however.

  Richard> No, I don't.

It is.  The biggest issue is unwinding across alternate signal stacks.
The changes needed to make this work are fairly extensive and I
decided against trying to backport them to the gcc unwinder (since
that would have likely introduced merging bugs).

	--david