libstdc++: [_GLIBCXX_DEBUG] Remove _Safe_container<>::_M_safe()

libstdc++: [_GLIBCXX_DEBUG] Remove _Safe_container<>::_M_safe()

_GLIBCXX_DEBUG container code cleanup to get rid of _Safe_container<>::_M_safe() and just
use _Safe:: calls which use normal inheritance. Also remove several usages of _M_base()
which can be most of the time ommitted and sometimes replace with explicit _Base::
calls.

libstdc++-v3/ChangeLog:

	* include/debug/safe_container.h (_Safe_container<>::_M_safe): Remove.
	* include/debug/deque (deque::operator=(initializer_list<>)): Replace
	_M_base() call with _Base:: call.
	(deque::operator[](size_type)): Likewise.
	* include/debug/forward_list (forward_list(forward_list&&, const allocator_type&)):
	Remove _M_safe() and _M_base() calls.
	(forward_list::operator=(initializer_list<>)): Remove _M_base() calls.
	(forward_list::splice_after, forward_list::merge): Likewise.
	* include/debug/list (list(list&&, const allocator_type&)):
	Remove _M_safe() and _M_base() calls.
	(list::operator=(initializer_list<>)): Remove _M_base() calls.
	(list::splice, list::merge): Likewise.
	* include/debug/map.h (map(map&&, const allocator_type&)):
	Remove _M_safe() and _M_base() calls.
	(map::operator=(initializer_list<>)): Remove _M_base() calls.
	* include/debug/multimap.h (multimap(multimap&&, const allocator_type&)):
	Remove _M_safe() and _M_base() calls.
	(multimap::operator=(initializer_list<>)): Remove _M_base() calls.
	* include/debug/set.h (set(set&&, const allocator_type&)):
	Remove _M_safe() and _M_base() calls.
	(set::operator=(initializer_list<>)): Remove _M_base() calls.
	* include/debug/multiset.h (multiset(multiset&&, const allocator_type&)):
	Remove _M_safe() and _M_base() calls.
	(multiset::operator=(initializer_list<>)): Remove _M_base() calls.
	* include/debug/string (basic_string(basic_string&&, const allocator_type&)):
	Remove _M_safe() and _M_base() calls.
	(basic_string::operator=(initializer_list<>)): Remove _M_base() call.
	(basic_string::operator=(const _CharT*), basic_string::operator=(_CharT)): Likewise.
	(basic_string::operator[](size_type), basic_string::operator+=(const basic_string&)):
	Likewise.
	(basic_string::operator+=(const _Char*), basic_string::operator+=(_CharT)): Likewise.
	* include/debug/unordered_map (unordered_map(unordered_map&&, const allocator_type&)):
	Remove _M_safe() and _M_base() calls.
	(unordered_map::operator=(initializer_list<>), unordered_map::merge):
	Remove _M_base() calls.
	(unordered_multimap(unordered_multimap&&, const allocator_type&)):
	Remove _M_safe() and _M_base() calls.
	(unordered_multimap::operator=(initializer_list<>), unordered_multimap::merge):
	Remove _M_base() calls.
	* include/debug/unordered_set (unordered_set(unordered_set&&, const allocator_type&)):
	Remove _M_safe() and _M_base() calls.
	(unordered_set::operator=(initializer_list<>), unordered_set::merge):
	Remove _M_base() calls.
	(unordered_multiset(unordered_multiset&&, const allocator_type&)):
	Remove _M_safe() and _M_base() calls.
	(unordered_multiset::operator=(initializer_list<>), unordered_multiset::merge):
	Remove _M_base() calls.
	* include/debug/vector (vector(vector&&, const allocator_type&)):
	Remove _M_safe() and _M_base() calls.
	(vector::operator=(initializer_list<>)): Remove _M_base() calls.
	(vector::operator[](size_type)): Likewise.