libstdc++: Fix std::deque::insert(pos, first, last) undefined behaviour [PR118035]

Inserting an empty range into a std::deque results in undefined calls to
either std::copy, std::copy_backward, std::move, or std::move_backward.
We call those algos with invalid arguments where the output range is the
same as the input range, e.g.  std::copy(first, last, first) which
violates the preconditions for the algorithms.

This fix simply returns early if there's nothing to insert. Most callers
already ensure that we don't even call _M_range_insert_aux with an empty
range, but some callers don't. Rather than checking for n == 0 in each
of the callers, this just does the check once and uses __builtin_expect
to treat empty insertions as unlikely.

libstdc++-v3/ChangeLog:

	PR libstdc++/118035
	* include/bits/deque.tcc (_M_range_insert_aux): Return
	immediately if inserting an empty range.
	* testsuite/23_containers/deque/modifiers/insert/118035.cc: New
	test.