[c++-pthreads] Restating the Jason model

[Alexander Terekhov]

Jason Merrill wrote:
[...]
> > Well, yes; although it also seems better to make one new rule for the new
> > "thread terminating exceptions" rather than two separate new rules.
> 
> There's no way to use the same rules for both, since we can't re-assert
> deferred exit.

Sure there's a way to use the same rules for both. Get rid of re-assert
for cancellation.

regards,
alexander.