Add Qt libs and headers

paho-mqtt3as-proxy/Qt/include/QtCore/qscopedvaluerollback.h

@@ -0,0 +1,47 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#ifndef QSCOPEDVALUEROLLBACK_H
+#define QSCOPEDVALUEROLLBACK_H
+
+#include <QtCore/qglobal.h>
+
+QT_BEGIN_NAMESPACE
+
+template <typename T>
+class [[nodiscard]] QScopedValueRollback
+{
+public:
+    explicit constexpr QScopedValueRollback(T &var)
+        : varRef(var), oldValue(var)
+    {
+    }
+
+    explicit constexpr QScopedValueRollback(T &var, T value)
+        : varRef(var), oldValue(qExchange(var, std::move(value)))
+    {
+    }
+
+#if __cpp_constexpr >= 201907L
+    constexpr
+#endif
+    ~QScopedValueRollback()
+    {
+        varRef = std::move(oldValue);
+    }
+
+    constexpr void commit()
+    {
+        oldValue = varRef;
+    }
+
+private:
+    T &varRef;
+    T oldValue;
+
+    Q_DISABLE_COPY_MOVE(QScopedValueRollback)
+};
+
+QT_END_NAMESPACE
+
+#endif // QSCOPEDVALUEROLLBACK_H