Add Qt libs and headers

paho-mqtt3as-proxy/Qt/include/QtCore/q20functional.h

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+// Copyright (C) 2021 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Marc Mutz <marc.mutz@kdab.com>
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+#ifndef Q20FUNCTIONAL_H
+#define Q20FUNCTIONAL_H
+
+#include <QtCore/qglobal.h>
+
+#include <functional>
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API. Types and functions defined in this
+// file can reliably be replaced by their std counterparts, once available.
+// You may use these definitions in your own code, but be aware that we
+// will remove them once Qt depends on the C++ version that supports
+// them in namespace std. There will be NO deprecation warning, the
+// definitions will JUST go away.
+//
+// If you can't agree to these terms, don't use these definitions!
+//
+// We mean it.
+//
+
+#include <functional>
+
+QT_BEGIN_NAMESPACE
+
+namespace q20 {
+// like std::identity
+#ifdef __cpp_lib_ranges
+using std::identity;
+#else
+struct identity
+{
+    struct is_transparent {};
+    template <typename T>
+    constexpr T &&operator()(T&& t) const noexcept { return std::forward<T>(t); }
+};
+#endif // __cpp_lib_ranges
+} // namespace q20
+
+QT_END_NAMESPACE
+
+#endif /* Q20FUNCTIONAL_H */