PR libstdc++/78595 implement insertion into maps in terms of emplace

PR libstdc++/78595 implement insertion into maps in terms of emplace

C++14 simplified the specification of the generic insert function
templates to be equivalent to calling emplace (or emplace_hint).
Defining them in terms of emplace takes care of the problems described
in PR 78595, ensuring a single conversion to value_type is done at the
right time.

	PR libstdc++/78595
	* include/bits/stl_map.h (map::insert(_Pair&&))
	(map::insert(const_iterator, _Pair&&)): Do emplace instead of insert.
	* include/bits/stl_multimap.h (multimap::insert(_Pair&&))
	(multimap::insert(const_iterator, _Pair&&)): Likewise.
	* include/bits/unordered_map.h (unordered_map::insert(_Pair&&))
	(unordered_map::insert(const_iterator, _Pair&&))
	(unordered_multimap::insert(_Pair&&))
	(unordered_multimap::insert(const_iterator, _Pair&&)): Likewise.
	* testsuite/23_containers/map/modifiers/insert/78595.cc: New test.
	* testsuite/23_containers/multimap/modifiers/insert/78595.cc: New test.
	* testsuite/23_containers/unordered_map/modifiers/78595.cc: New test.
	* testsuite/23_containers/unordered_multimap/modifiers/78595.cc: New
	test.

From-SVN: r264059