[Bug libstdc++/51365] cannot use final empty class in std::tuple

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51365

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-11-30 23:35:00 UTC ---
Created attachment 25963
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25963
fix other parts of library

here's a proof of concept patch showing how to fix existing code that inherits
from allocators so that it is ABI-compatible for non-final allocators and also
supports final allocators (by inheriting from a wrapper class instead). 
Something like this needs to be done for the containers so they stay backwards
compatible but also work with final types.

(I decided to rename the intrinsic to __is_final and that's what this patch
uses)