Backport PR #161859 to libcxx to allow abseil update

This backports [PR #161859](llvm/llvm-project#161859) from upstream.
commit_hash:55593669b4c3a7dd0109530c3cd78abff067c1f7

Author: georgthegreat

contrib/libs/cxxsupp/libcxx/include/__ranges/lazy_split_view.h

@@ -75,6 +75,7 @@ class lazy_split_view : public view_interface<lazy_split_view<_View, _Pattern>>
   using _MaybeCurrent = _If<!forward_range<_View>, __non_propagating_cache<iterator_t<_View>>, __empty_cache>;
   _LIBCPP_NO_UNIQUE_ADDRESS _MaybeCurrent __current_ = _MaybeCurrent();
 
+private:
   template <bool>
   struct __outer_iterator;
   template <bool>