Update json_writer.cpp

Author: mananel

src/lib_json/json_writer.cpp

@@ -72,10 +72,12 @@
 #define isnan(x) (x != x)
 #endif
 
+#if !defined(__APPLE__)
 #if !defined(isfinite)
 #define isfinite finite
 #endif
 #endif
+#endif
 
 #if defined(_MSC_VER) && _MSC_VER >= 1400 // VC++ 8.0
 // Disable warning about strdup being deprecated.