Define _AT_NULL_PATHNAME_ALLOWED

Cygwin needs an internal flag to allow specifying an empty pathname
in utimesat (GLIBC extension). We define it in _default_fcntl.h to
make sure we never introduce a value collision accidentally.
While at it, define the values as 16 bit hex values.

Reviewed-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

newlib/libc/include/sys/_default_fcntl.h

@@ -162,12 +162,13 @@ extern "C" {
 #define AT_FDCWD -2
 
 /* Flag values for faccessat2) et al. */
-#define AT_EACCESS              1
-#define AT_SYMLINK_NOFOLLOW     2
-#define AT_SYMLINK_FOLLOW       4
-#define AT_REMOVEDIR            8
+#define AT_EACCESS                 0x0001
+#define AT_SYMLINK_NOFOLLOW        0x0002
+#define AT_SYMLINK_FOLLOW          0x0004
+#define AT_REMOVEDIR               0x0008
 #if __GNU_VISIBLE
-#define AT_EMPTY_PATH          16
+#define AT_EMPTY_PATH              0x0010
+#define _AT_NULL_PATHNAME_ALLOWED  0x4000 /* Internal flag used by futimesat */
 #endif
 #endif