PR libstdc++/92267 fix ABI change in deque iterators

PR libstdc++/92267 fix ABI change in deque iterators

Defaulting the copy constructor on its first declaration made it change
from user-provided (and non-trivial) to implicitly-defined (and
trivial). This caused an ABI incompatibility between GCC 8 and GCC 9,
where functions taking a deque iterator disagree on the argument passing
convention.

Backport from mainline
2019-10-29  Jonathan Wakely  <jwakely@redhat.com>

	PR libstdc++/92267
	* include/bits/stl_deque.h (_Deque_iterator(const _Deque_iterator&)):
	Do not define as defaulted.
	* testsuite/23_containers/deque/types/92267.cc: New test.