ghook: Ensure all bits are named in GHookFlagMask

This is to avoid the Wflag-enum warning that Clang emits when you have a
flags enum where a multi-bit value encompasses a bit that doesn't have a
corresponding single-bit value.

glib/ghook.h

@@ -56,6 +56,8 @@ typedef enum
 {
   G_HOOK_FLAG_ACTIVE	    = 1 << 0,
   G_HOOK_FLAG_IN_CALL	    = 1 << 1,
+  G_HOOK_FLAG_RESERVED1     = 1 << 2, /*< private >*/
+  G_HOOK_FLAG_RESERVED2     = 1 << 3, /*< private >*/
   G_HOOK_FLAG_MASK	    = 0x0f
 } G_GNUC_FLAG_ENUM GHookFlagMask;
 #define G_HOOK_FLAG_USER_SHIFT	(4)