PR libstdc++/80893 Fix null dereference in vector<bool>

PR libstdc++/80893 Fix null dereference in vector<bool>

Backport from mainline
2017-06-17  Jonathan Wakely  <jwakely@redhat.com>

	PR libstdc++/80893
	* testsuite/23_containers/vector/bool/80893.cc: Add { target c++11 }.

Backport from mainline
2017-05-31  Jonathan Wakely  <jwakely@redhat.com>

	PR libstdc++/80893
	* include/bits/stl_bvector.h (vector<bool>::_M_initialize): Avoid
	null pointer dereference when size is zero.
	* testsuite/23_containers/vector/bool/80893.cc: New.
	* testsuite/util/testsuite_allocator.h (PointerBase::PointerBase):
	Add non-explicit constructor from nullptr.
	(PointerBase::derived() const): Add const-qualified overload.

From-SVN: r263381