include/linux/sem.h: make sysv_sem empty if SYSVIPC is disabled

For the sysvsem undo, each task struct contains a sysv_sem structure with
a pointer to the undo information.

This pointer is only necessary if sysvipc is enabled - thus the pointer
can be made conditional on CONFIG_SYSVIPC.

Signed-off-by: Manfred Spraul <[e-mail]>
Acked-by: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Mike Galbraith <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/sem.h

···
 	int			complex_count;	/* pending complex operations */
 };
 
+#ifdef CONFIG_SYSVIPC
+
 struct sysv_sem {
 	struct sem_undo_list *undo_list;
 };
-
-#ifdef CONFIG_SYSVIPC
 
 extern int copy_semundo(unsigned long clone_flags, struct task_struct *tsk);
 extern void exit_sem(struct task_struct *tsk);
 
 #else
+
+struct sysv_sem {
+	/* empty */
+};
+
 static inline int copy_semundo(unsigned long clone_flags, struct task_struct *tsk)
 {
 	return 0;