[PATCH glibc 8/9] support: implement xpthread key create/delete (v4)

[Florian Weimer]

* Mathieu Desnoyers via Libc-alpha:

> diff --git a/support/xthread.h b/support/xthread.h
> index d350d1506d..2a519874bf 100644
> --- a/support/xthread.h
> +++ b/support/xthread.h
> @@ -95,6 +95,8 @@ void xpthread_rwlock_wrlock (pthread_rwlock_t *rwlock);
>  void xpthread_rwlock_rdlock (pthread_rwlock_t *rwlock);
>  void xpthread_rwlock_unlock (pthread_rwlock_t *rwlock);
>  void xpthread_rwlock_destroy (pthread_rwlock_t *rwlock);
> +void xpthread_key_create (pthread_key_t *key, void (*destr_function) (void *));
> +void xpthread_key_delete (pthread_key_t key);

I think xpthread_key_create should return the pthread_key_t result
directly.  It's similar to what we did for xpthread_create.

Please also update for the year 2020.