[v3] libstdc++/17922

[Paolo Carlini]

Benjamin Kosnik wrote:

>Here's something we can try to eliminate some of this issue.
>  
>
Yes, thanks for working on this!

... and sorry for not not having replied sooner to your hint in the 
audit trail: I was sad because of the _S_ios_openmode_end & co bits, 
that probably we can't really fix within the current ABI: for v7 maybe 
we should bite the bullet and renounce to the enums?!?

Paolo.