[Bug libstdc++/64658] std::atomic_init() undefined

[Jon Chesterfield]

> --- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
> fixed - probably not worth backporting since noone has noticed it's missing


For what it's worth, at least one of your users (me) has noticed this. 
I'll restructure code as necessary to use the constructor instead, i.e. 
std::atomic<std::size_t> foo(0);

Regards,

Jon