libstdc++: Fix memory leak in std::barrier destructor [PR123378]

When I replaced the std::unique_ptr member in r16-997-gef632273a90657 I
should have added an explicit delete[] operation to replace the effects
of the unique_ptr destructor.

libstdc++-v3/ChangeLog:

	PR libstdc++/123378
	* include/std/barrier (~__tree_barrier_base): Define.

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

libstdc++-v3/include/std/barrier

@@ -114,6 +114,12 @@ It looks different from literature pseudocode for two main reasons:
 	_M_state.store(_M_alloc_state().release(), memory_order_release);
     }
 
+    ~__tree_barrier_base()
+    { delete[] _M_state.load(memory_order_relaxed); }
+
+    __tree_barrier_base(const __tree_barrier_base&&) = delete;
+    __tree_barrier_base& operator=(const __tree_barrier_base&&) = delete;
+
     unique_ptr<__state_t[]>
     _M_alloc_state()
     {