(ixwebsocket) use a C++11 compatible make_unique shim

ixwebsocket/IXUniquePtr.h

@@ -0,0 +1,18 @@
+/*
+ *  IXUniquePtr.h
+ *  Author: Benjamin Sergeant
+ *  Copyright (c) 2020 Machine Zone, Inc. All rights reserved.
+ */
+
+#pragma once
+
+#include <memory>
+
+namespace ix
+{
+    template<typename T, typename... Args>
+    std::unique_ptr<T> make_unique(Args&&... args)
+    {
+        return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
+    }
+} // namespace ix