libstdc++: fix element construction in std::deque::emplace [PR118087]

libstdc++: fix element construction in std::deque::emplace [PR118087]

In order to emplace a value in the middle of a deque, a temporary was
previously constructed directly with __args... in _M_emplace_aux.
This would not work since std::deque is allocator-aware and should
construct elements with _Alloc_traits::construct instead before the
element is moved.

Using the suggestion in PR118087, we can define _Temporary_value
similar to the one used in std::vector, so the temporary can be
constructed with uses-allocator construction.

	PR libstdc++/118087

libstdc++-v3/ChangeLog:

	* include/bits/deque.tcc: Use _Temporary_value in
	_M_emplace_aux.
	* include/bits/stl_deque.h: Introduce _Temporary_value.
	* testsuite/23_containers/deque/modifiers/emplace/118087.cc:
	New test.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Signed-off-by: Ben Wu <soggysocks206@gmail.com>