[Bug libstdc++/62313] Data race in debug iterators

[François Dumont]

>> Apart from those minor adjustments I think this looks good, but I'd
>> like to know that it has been tested with -fsanitize=thread, even if
>> only lightly tested.
>>
>>

Hi

     Dmitry, who reported the bug, confirmed the fix. Can I go ahead and 
commit ?

François