[Patch] Fix libstdc++/10097

[Paolo Carlini]

Benjamin Kosnik wrote:

>>Indeed, Benjamin, you can count on my help. I will do 21, in parallel 
>>with 27, after the last pending commits affecting 27, before 
>>libstdc++/9701 and the other 27_io PRs, which will wait for a 
>>restructured testsuite.
>>    
>>
>Great. I really appreciate this. I'll start working on the 27_io redo
>today. In general, follow the ideas in the 22_locale organization where
>possible. If you have questions, or are uncertain, please feel free to
>ask. For the most part, I think it's pretty straightforward.
>
Indeed. 27_io its bigger and a little bit more tricky somewhere.

Anyway, I'm already half way through my 21, I hope to send you the 
tarball before the end of day.

Thanks to you for coordinating our adventure,
Paolo.