PR libstdc++/56267
	* include/bits/hashtable_policy.h (_Hash_code_base<... false>): Grant
	friendship to _Local_iterator_base<..., false>.
	(_Local_iterator_base): Give protected access to all existing members.
	(_Local_iterator_base::_M_curr()): New public accessor.
	(_Local_iterator_base::_M_get_bucket()): New public accessor.
	(_Local_iterator_base<..., false>::_M_init()): New function to manage
	the lifetime of the _Hash_code_base explicitly.
	(_Local_iterator_base<..., false>::_M_destroy()): Likewise.
	(_Local_iterator_base<..., false>): Define copy constructor and copy
	assignment operator that use new functions to manage _Hash_code_base.
	(operator==(const _Local_iterator_base&, const _Local_iterator_base&),
	operator==(const _Local_iterator_base&, const _Local_iterator_base&)):
	Use public API for _Local_iterator_base.
	* include/debug/safe_local_iterator.h (_Safe_local_iterator): Likewise.
	* include/debug/unordered_map (__debug::unordered_map::erase(),
	__debug::unordered_multimap::erase()): Likewise.
	* include/debug/unordered_set (__debug::unordered_set::erase(),
	__debug::unordered_multiset::erase()): Likewise.
	* testsuite/23_containers/unordered_set/56267-2.cc: New test.

From-SVN: r206834