On VS 2013 and newer, actually use strtoll instead of redefining it to _strtoi64.

json_util.c

@@ -39,7 +39,10 @@
 #endif /* HAVE_UNISTD_H */
 
 #ifdef WIN32
-# define strtoll _strtoi64
+# if MSC_VER < 1800
+/* strtoll is available only since Visual Studio 2013 */
+#  define strtoll _strtoi64
+# endif
 # define WIN32_LEAN_AND_MEAN
 # include <windows.h>
 # include <io.h>