Use autoconf, not gcc version, to decide which warnings we have

This gives more accurate results under Clang, which can only help us
detect more warnings in more places.

Fixes bug 19216; bugfix on 0.2.0.1-alpha

src/or/config.c

@@ -2683,7 +2683,7 @@ options_validate_cb(void *old_options, void *options, void *default_options,
 
 #define REJECT(arg) \
   STMT_BEGIN *msg = tor_strdup(arg); return -1; STMT_END
-#ifdef __GNUC__
+#if defined(__GNUC__) && __GNUC__ <= 3
 #define COMPLAIN(args...) \
   STMT_BEGIN log_warn(LD_CONFIG, args); STMT_END
 #else