mutex: Fix up mutex_waiter usage

The patch moving bits into mutex.c was a little too much; by also
moving struct mutex_waiter a few less common CONFIGs would no longer
build.

Fixes: 5f35d5a6 ("locking/mutex: Make __mutex_owner static to mutex.c")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

include/linux/mutex.h

@@ -65,6 +65,19 @@ struct mutex {
 #endif
 };
 
+/*
+ * This is the control structure for tasks blocked on mutex,
+ * which resides on the blocked task's kernel stack:
+ */
+struct mutex_waiter {
+	struct list_head	list;
+	struct task_struct	*task;
+	struct ww_acquire_ctx	*ww_ctx;
+#ifdef CONFIG_DEBUG_MUTEXES
+	void			*magic;
+#endif
+};
+
 #ifdef CONFIG_DEBUG_MUTEXES
 
 #define __DEBUG_MUTEX_INITIALIZER(lockname)				\

kernel/locking/mutex.c

@@ -36,19 +36,6 @@
 # include "mutex.h"
 #endif
 
-/*
- * This is the control structure for tasks blocked on mutex,
- * which resides on the blocked task's kernel stack:
- */
-struct mutex_waiter {
-	struct list_head	list;
-	struct task_struct	*task;
-	struct ww_acquire_ctx	*ww_ctx;
-#ifdef CONFIG_DEBUG_MUTEXES
-	void			*magic;
-#endif
-};
-
 void
 __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
 {

kernel/locking/mutex.h

@@ -19,8 +19,6 @@
 #define debug_mutex_unlock(lock)			do { } while (0)
 #define debug_mutex_init(lock, name, key)		do { } while (0)
 
-struct mutex_waiter;
-
 static inline void
 debug_mutex_lock_common(struct mutex *lock, struct mutex_waiter *waiter)
 {