Ignore jansson.h's -Wunused-function for GCC too.
#if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
#pragma GCC diagnostic push
#endif
+#pragma GCC diagnostic ignored "-Wunused-function"
#pragma GCC diagnostic ignored "-Wunreachable-code"
#elif defined(__clang__)
#pragma clang diagnostic push
