[PATCH 22/22] nptl: Remove ATOMIC_EXCHANGE_USES_CAS usage

[Wilco Dijkstra]

Hi Adhemerval,
 
> The only usage was for pthread_spin_lock, introduced by 12d2dd706099aa4,
> as a way to optimize the code for certain architectures. Now that atomic
> builtins are used by default, let the compiler use the best code sequence
> for the atomic exchange.
>
> Co-authored-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

LGTM.

Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>

Cheers,
Wilco