Fix: Check if __GNUCC__ is defined

This has been detected via MSVC's Warning C4668

cJSON.c

@@ -1849,7 +1849,7 @@ CJSON_PUBLIC(void) cJSON_AddItemToObject(cJSON *object, const char *string, cJSO
     item->type &= ~cJSON_StringIsConst;
 }
 
-#if defined (__clang__) || ((__GNUC__)  && ((__GNUC__ > 4) || ((__GNUC__ == 4) && (__GNUC_MINOR__ > 5))))
+#if defined(__clang__) || (defined(__GNUC__)  && ((__GNUC__ > 4) || ((__GNUC__ == 4) && (__GNUC_MINOR__ > 5))))
     #pragma GCC diagnostic push
 #endif
 #ifdef __GNUC__
@@ -1871,7 +1871,7 @@ CJSON_PUBLIC(void) cJSON_AddItemToObjectCS(cJSON *object, const char *string, cJ
     item->type |= cJSON_StringIsConst;
     cJSON_AddItemToArray(object, item);
 }
-#if defined (__clang__) || ((__GNUC__)  && ((__GNUC__ > 4) || ((__GNUC__ == 4) && (__GNUC_MINOR__ > 5))))
+#if defined(__clang__) || (defined(__GNUC__)  && ((__GNUC__ > 4) || ((__GNUC__ == 4) && (__GNUC_MINOR__ > 5))))
     #pragma GCC diagnostic pop
 #endif