STYLE: Pefer = default to explicitly trivial implementations

This check replaces default bodies of special member functions with
= default;. The explicitly defaulted function declarations enable more
opportunities in optimization, because the compiler might treat
explicitly defaulted functions as trivial.

Additionally, the C++11 use of = default more clearly expreses the
intent for the special member functions.

SRCDIR=/Users/johnsonhj/src/jsoncpp/ #My local SRC
BLDDIR=/Users/johnsonhj/src/jsoncpp/cmake-build-debug/ #My local BLD

cd /Users/johnsonhj/src/jsoncpp/cmake-build-debug/
run-clang-tidy.py -extra-arg=-D__clang__ -checks=-*,modernize-use-equals-default  -header-filter=.* -fix

include/json/writer.h

@@ -169,7 +169,7 @@ class JSONCPP_DEPRECATED("Use StreamWriterBuilder instead") JSON_API FastWriter
     : public Writer {
 public:
   FastWriter();
-  ~FastWriter() override {}
+  ~FastWriter() override = default;
 
   void enableYAMLCompatibility();
 
@@ -229,7 +229,7 @@ class JSONCPP_DEPRECATED("Use StreamWriterBuilder instead") JSON_API
     StyledWriter : public Writer {
 public:
   StyledWriter();
-  ~StyledWriter() override {}
+  ~StyledWriter() override = default;
 
 public: // overridden from Writer
   /** \brief Serialize a Value in <a HREF="http://www.json.org">JSON</a> format.