[PATCH 1/2] posix: Correctly enable/disable cancellation on Linux posix_spawn

[Florian Weimer]

* Adhemerval Zanella:

>> Don't you have to try this multiple times, to see if you can hit the
>> race?
>
> Not in this test because the idea is to check if posix_spawn acts or not
> on a pending cancellation, not if an asynchronous cancellation cancels the
> thread while the thread executes posix_spawn.

Ah, I'm still trying to wrap my head around the different forms of
cancellation.  Patch is good as-is then.  Thanks.