fd_util: fd_set_cloexec() returns a value on WIN32

This function is empty on WIN32, but we need to return a value.

src/fd_util.c

@@ -75,6 +75,8 @@ fd_set_cloexec(int fd, bool enable)
 #else
 	(void)fd;
 	(void)enable;
+
+	return 0;
 #endif
 }