[patch] add __is_final trait to fix libstdc++/51365

[Paolo Carlini]

On 12/11/2011 04:05 PM, Jonathan Wakely wrote:
> ping
In my opinion __is_final would be definitely useful in general, for 4.8, 
and 4.7 too, if isn't too late.

As regards the wider issue which is being discussed on the reflector - 
beware, I didn't follow all the messages - 'final' disabling a nice 
optimization like EBO makes me very nervous. Really, doesn't seem part 
of the intended general philosophy in this area. There must be a way to 
overcome the annoyance. Last resort, if suggestions like having 'final' 
not forbidding private derivation cannot go through, we could imagine a 
GCC attribute reverting the effect of 'final' for people (library 
writers ;) knowing what they are doing. I don't know.

Paolo.