[Patch] Fix libstdc++/12352

[Paolo Carlini]

Pétur Runólfsson wrote:

[snip]

>This should be detectable with the testcase I attached to the PR
>if the outer loop is run often enough.
>
Thanks.

As I wrote, I didn't hope to fix *all* the problems, unfortunately...

However, I tried your testcase with a command line parameter up to 
~1000-3000 and nothing happened. I would appreciate if you could prepare 
a more sensitive testcase and perhaps file a different PR, in order to 
better keep track of the issue: in the next days I would like to work on 
a few other PR before returning to excpetion safety.

Thanks again,
Paolo.