[PATCH][_Hashtable] Fix insertion of range of type convertible to value_type PR 56112

[François Dumont]

Gentle reminder, it is important to have this for gcc 12.

On 15/02/22 10:05, François Dumont wrote:
> We have a regression regarding management of types convertible to 
> value_type. It is an occurrence of PR 56112 but for the insert method.
>
>     libstdc++: [_Hashtable] Insert range of types convertible to 
> value_type PR 56112
>
>     Fix insertion of range of types convertible to value_type.
>
>     libstdc++-v3/ChangeLog:
>
>             PR libstdc++/56112
>             * include/bits/hashtable.h
>             (_Hashtable<>::_M_insert_unique_aux): New.
>             (_Hashtable<>::_S_to_value): New.
>             (_Hashtable<>::_M_insert(_Arg&&, const _NodeGenerator&, 
> true_type)): Use latters.
>             * testsuite/23_containers/unordered_map/cons/56112.cc: Use 
> dg-do compile.
>             * testsuite/23_containers/unordered_set/cons/56112.cc: New 
> test.
>
> Tested under Linux x86_64.
>
> Ok to commit ?
>
> François