add required libraries

external/include/json/forwards.h

@@ -0,0 +1,43 @@
+// Copyright 2007-2010 Baptiste Lepilleur and The JsonCpp Authors
+// Distributed under MIT license, or public domain if desired and
+// recognized in your jurisdiction.
+// See file LICENSE for detail or copy at http://jsoncpp.sourceforge.net/LICENSE
+
+#ifndef JSON_FORWARDS_H_INCLUDED
+#define JSON_FORWARDS_H_INCLUDED
+
+#if !defined(JSON_IS_AMALGAMATION)
+#include "config.h"
+#endif // if !defined(JSON_IS_AMALGAMATION)
+
+namespace Json {
+
+// writer.h
+class StreamWriter;
+class StreamWriterBuilder;
+class Writer;
+class FastWriter;
+class StyledWriter;
+class StyledStreamWriter;
+
+// reader.h
+class Reader;
+class CharReader;
+class CharReaderBuilder;
+
+// json_features.h
+class Features;
+
+// value.h
+using ArrayIndex = unsigned int;
+class StaticString;
+class Path;
+class PathArgument;
+class Value;
+class ValueIteratorBase;
+class ValueIterator;
+class ValueConstIterator;
+
+} // namespace Json
+
+#endif // JSON_FORWARDS_H_INCLUDED