Merge pull request microsoft#1520 from sighingnow/ht/std_format_macro

Define __STDC_FORMAT_MACROS when it hasn't been defined to avoid duplicate define error.

Author: Charlie Barto

Release/src/json/json_serialization.cpp

@@ -16,7 +16,9 @@
 #include <stdio.h>
 
 #ifndef _WIN32
+#ifndef __STDC_FORMAT_MACROS
 #define __STDC_FORMAT_MACROS
+#endif
 #include <inttypes.h>
 #endif