Centralize owning, non-shared pointer test.

Author: rpavlik

src/lib_json/json_reader.cpp

@@ -43,7 +43,7 @@ static int       stackDepth_g = 0;  // see readValue()
 
 namespace Json {
 
-#if __GNUC__ >= 6
+#if defined(JSON_USE_SCOPED_PTR)
 typedef std::scoped_ptr<CharReader> const  CharReaderPtr;
 #else
 typedef std::auto_ptr<CharReader>          CharReaderPtr;

src/lib_json/json_tool.h

@@ -12,6 +12,10 @@
  * It is an internal header that must not be exposed.
  */
 
+#if defined(__GNUC__) && (__GNUC__ >= 6)
+#define JSON_USE_SCOPED_PTR
+#endif
+
 namespace Json {
 
 /// Converts a unicode code-point to UTF-8.

src/lib_json/json_writer.cpp

@@ -54,7 +54,7 @@
 
 namespace Json {
 
-#if __GNUC__ >= 6
+#if defined(JSON_USE_SCOPED_PTR)
 typedef std::scoped_ptr<StreamWriter> const  StreamWriterPtr;
 #else
 typedef std::auto_ptr<StreamWriter>          StreamWriterPtr;