C2766 explicit specialization; 'specialization' has already been defined when compiling on Visual Studio with /Zc:__cplusplus flag

Created by: archieLa

Since Visual Studio 2017 when /Zc:__cplusplus flag is used then the __cplusplus macro is evaluated correctly based on C++ standard used. When that happens the C2766 occurs since both ARDUINOJSON_HAS_LONG_LONG and ARUDINO_HAS_INT_64 are evaluated to be true and cause duplicate template specialization https://github.com/bblanchon/ArduinoJson/blob/daa279d57b20736ba3bf39de935fa919661d8ecf/src/ArduinoJson/Configuration.hpp#L8