re PR libstdc++/83709 (Inserting duplicates into an unordered associative containers causes the container to invalidate iterators)

2018-01-09  François Dumont  <fdumont@gcc.gnu.org>

	PR libstdc++/83709
	* include/bits/hashtable_policy.h
	(__distance_fwd(_Iterator, _Iterator, input_iterator_tag)): Return 1 if
	__first != __last.
	(_Insert_base::_M_insert_range(_Ite, _Ite, _NodeGetter, true_type)): New.
	(_Insert_base::_M_insert_range(_Ite, _Ite, _NodeGetter, false_type)):
	Add false_type parameter.
	(_Insert_base::insert): Adapt.
	* include/bits/hashtable.h (_Hashtable::operator=(initializzr_list<>)):
	Adapt.
	(_Hashtable::_M_insert(_Arg&&, const _NodeGen&, true_type, size_t)):
	 Add __n_elt parameter, defaulted to 1.
	(_Hashtable::_M_insert_unique_node): Likewise. Use it to call rehash
	policy _M_need_rehash.
	(_Hashtable::_M_merge_unique): Pass target number of elements to add to
	produce only 1 rehash if necessary.
	* testsuite/23_containers/unordered_map/insert/83709.cc: New.
	* testsuite/23_containers/unordered_set/insert/83709.cc: New.

From-SVN: r256396