libstdc++: Fix std::vector::append_range for overlapping ranges

libstdc++: Fix std::vector::append_range for overlapping ranges

Unlike insert_range and assign_range, the append_range function does not
have a precondition that the range doesn't overlap *this. That means we
need to avoid relocating the existing elements until after copying from
the range. This means I need to revert r15-8488-g3e1d760bf49d0e which
made the from_range_t constructor use append_range, because the
constructor can avoid the additional complexity needed by append_range.
When relocating the existing elements in append_range we can use
std::__relocate_a to do it more efficiently, if that's valid.

std::vector<bool>::append_range needs similar treatment, although it's a
bit simpler as we know that the elements are trivially copyable and so
we don't need to worry about them throwing. assign_range doesn't allow
overlapping ranges, so can be rewritten to be more efficient than
calling append_range for the forward or sized range case.

libstdc++-v3/ChangeLog:

	* include/bits/stl_bvector.h (vector::assign_range): More
	efficient implementation for forward/sized ranges.
	(vector::append_range): Handle potentially overlapping range.
	* include/bits/stl_vector.h (vector(from_range_t, R&&, Alloc)):
	Do not use append_range for non-sized input range case.
	(vector::append_range): Handle potentially overlapping range.
	* include/bits/vector.tcc (vector::insert_range): Forward range
	instead of moving it.
	* testsuite/23_containers/vector/bool/modifiers/insert/append_range.cc:
	Test overlapping ranges.
	* testsuite/23_containers/vector/modifiers/append_range.cc:
	Likewise.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>