PR77528 partially revert r244278 and define default constructors
PR libstdc++/77528
* include/bits/stl_queue.h (queue, priority_queue): Remove default
member-initializers and define default constructors as templates with
constraints.
* include/bits/stl_stack.h (stack): Likewise.
* testsuite/23_containers/priority_queue/requirements/constructible.cc:
New.
* testsuite/23_containers/priority_queue/requirements/
explicit_instantiation/1.cc: Test more instantiations.
* testsuite/23_containers/priority_queue/requirements/
explicit_instantiation/1_c++98.cc: Likewise.
* testsuite/23_containers/queue/requirements/constructible.cc: New.
* testsuite/23_containers/stack/requirements/constructible.cc: New.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@244374 138bc75d-0d04-0410-961f-82ee72b054a4