There is no need to use an allocator of the correct value_type when
calling allocator_traits::construct and allocator_traits::destroy. The
existing node allocator can be used, instead of constructing a new
allocator object every time.
There's also no benefit to using __gnu_cxx::__alloc_traits instead of
std::allocator_traits to get the pointer and const_pointer types.
std::forward_list is only available for C++11 and later, when
std::allocator_traits is available too.
PR libstdc++/86127
* include/bits/forward_list.h (_Fwd_list_base::_Tp_alloc_type): Remove
unused typedef.
(_Fwd_list_base::_Node_alloc_traits): Use allocator_traits instead of
__gnu_cxx::__alloc_traits.
(_Fwd_list_base::_M_create_node, _Fwd_list_base::_M_erase_after):
Use node allocator to create and destroy elements.
(forward_list::_Tp_alloc_type): Remove unused typedef.
(forward_list::_Alloc_traits): Use allocator_traits instead of
__gnu_cxx::__alloc_traits.
From-SVN: r261554
