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 <manfred@colorfullife.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/sem.h

@@ -96,16 +96,21 @@ struct sem_array {
 	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;