+#if !_LIBC
+/* Return non-zero if FD is open. */
+static int
+is_open (int fd)
+{
+# if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
+ /* On native Windows: The initial state of unassigned standard file
+ descriptors is that they are open but point to an INVALID_HANDLE_VALUE.
+ There is no fcntl, and the gnulib replacement fcntl does not support
+ F_GETFL. */
+ return (HANDLE) _get_osfhandle (fd) != INVALID_HANDLE_VALUE;
+# else
+# ifndef F_GETFL
+# error Please port fcntl to your platform
+# endif
+ return 0 <= fcntl (fd, F_GETFL);
+# endif
+}
+#endif
+
+static void