Async cacellation and pthread_cleanup_push

[Florian Weimer]

* Andreas Schwab:

> On Aug 23 2021, Florian Weimer wrote:
>
>> GCC should ignore __attribute__ ((nothrow)) with -fnon-call-exceptions.
>
> Wouldn't help the test case since it doesn't use -fnon-call-exceptions.

I see, thanks.

We should probably take this to the GCC developers.  Or give up entirely
on asynchronous cancellation.

Florian