libstdc++: Fix tests relying on operator new/delete overload

libstdc++: Fix tests relying on operator new/delete overload

Fix tests that are checking for an expected allocation plan. They are failing if
an allocation is taking place outside the test main.

libstdc++-v3/ChangeLog

	* testsuite/util/replacement_memory_operators.h
	(counter::scope): New, capture and reset counter count at construction and
	restore it at destruction.
	(counter::check_new): Add scope instantiation.
	* testsuite/23_containers/unordered_map/96088.cc (main):
	Add counter::scope instantiation.
	* testsuite/23_containers/unordered_multimap/96088.cc (main): Likewise.
	* testsuite/23_containers/unordered_multiset/96088.cc (main): Likewise.
	* testsuite/23_containers/unordered_set/96088.cc (main): Likewise.
	* testsuite/ext/malloc_allocator/deallocate_local.cc (main): Likewise.
	* testsuite/ext/new_allocator/deallocate_local.cc (main): Likewise.
	* testsuite/ext/throw_allocator/deallocate_local.cc (main): Likewise.
	* testsuite/ext/pool_allocator/allocate_chunk.cc (started): New global.
	(operator new(size_t)): Check started.
	(main): Set/Unset started.
	* testsuite/17_intro/no_library_allocation.cc: New test case.