Fix #230: must be GNUC >= 5

src/civetweb.c

@@ -1254,7 +1254,7 @@ mg_atomic_inc(volatile int *addr)
 	 * so whatever you use, the other SDK is likely to raise a warning. */
 	ret = InterlockedIncrement((volatile long *)addr);
 #elif defined(__GNUC__)                                                        \
-    && (__GNUC__ > 5 || (__GNUC__ == 4 && __GNUC_MINOR__ > 0))
+    && (__GNUC__ >= 5 || (__GNUC__ == 4 && __GNUC_MINOR__ > 0))
 	ret = __sync_add_and_fetch(addr, 1);
 #else
 	ret = (++(*addr));