PR libstdc++/71964
	* include/bits/basic_string.h [_GLIBCXX_USE_CXX11_ABI]
	(basic_string::_Alloc_hider(pointer, _Alloc&&)): Add constructor.
	* include/bits/stl_tree.h (_Rb_tree(_Rb_tree&&)): Move allocator.
	* testsuite/21_strings/basic_string/allocator/71964.cc: New test.
	* testsuite/23_containers/set/allocator/71964.cc: New test.

From-SVN: r238647