[patch] Fix libstdc++/36962

[Paolo Carlini]

Hi,
> Something like (untested, sorry)
>
>    D d;
>    std::unique_ptr<T,D&> p1( new T, d );
>
>    std::shared_ptr<T> p2( std::move( p1 ) );
>
>    typedef std::reference_wrapper<D> D2;
>    D2 * p3 = std::get_deleter<D2>( p2 );
>
>    assert( p3 != 0 );
>    assert( &p3->get() == &d );
Yes, this one "works", in the sense that if I apply my patchlet the 
first assert fails at run-time.

Thanks a lot, I will add it to the testsuite!
Paolo.