[Bug libstdc++/85222] [7/8 Regression] ABI breakage of __throw_ios_failure by r244498

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85222

--- Comment #19 from Richard Biener <rguenth at gcc dot gnu.org> ---
Luckily both failure classes are immutable (via access limitations) so the
following issue with the __dual_ios_failure idea doesn't exist:

 catch (old-ABI &e)
   {
     modify e in-place
     throw;
   }
 ...
 catch (new-ABI &e)
   {
     ... expect modified content ...
   }