[Bug libstdc++/54005] Use __atomic_always_lock_free in libstdc++ is_lock_free instead of __atomic_is_lock_free

[hp at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54005

--- Comment #23 from Hans-Peter Nilsson <hp at gcc dot gnu.org> ---
(In reply to Hans-Peter Nilsson from comment #22)
> Anyway, as per the arguments in n2992.html in the link above, I (still)
> think __atomic_*always*_lock free should be used instead; this'd make the
> intent clear.

...and also, a call might be generated as the result of using
__atomic_is_lock_free (instead of __atomic_always_lock_free), so the target may
change its mind.  Not good.