[libc++] NFC: Add a simple test to make sure we destroy elements in std::list

[ldionne]

Submitting a review just to run CI really.

[• Quuxplusone]

:)

[Mordante]

Nice to see this test!

libcxx/test/std/containers/sequences/list/list.cons/dtor.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// <list>
+
+// ~list()
+
+#include <list>
+#include <cassert>
+#include <set>
+
+#include "test_macros.h"
+
+
+std::set<int> destroyed;
+
+struct Foo {
+    explicit Foo(int i) : value(i) { }
+    ~Foo() { destroyed.insert(value); }
+    int value;
+};
+
+int main(int, char**)
+{
+    {
+        std::list<Foo> list;
+        list.emplace_back(1);
+        list.emplace_back(2);
+        list.emplace_back(3);
+        assert(destroyed.empty());
+    }
+    assert(destroyed.count(1) == 1);
+    assert(destroyed.count(2) == 1);
+    assert(destroyed.count(3) == 1);
+
+    return 0;
+}