sched/headers: Make all include/linux/sched/*.h headers build standalone

Make each header self-sufficient, so that it can be built successfully
both in an allnoconfig and allyesconfig kernel.

Also standardize the naming of their header guards.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/sched/rt.h

@@ -1,7 +1,9 @@
-#ifndef _SCHED_RT_H
-#define _SCHED_RT_H
+#ifndef _LINUX_SCHED_RT_H
+#define _LINUX_SCHED_RT_H
 
-#include <linux/sched/prio.h>
+#include <linux/sched.h>
+
+struct task_struct;
 
 static inline int rt_prio(int prio)
 {
@@ -57,4 +59,4 @@ extern void normalize_rt_tasks(void);
  */
 #define RR_TIMESLICE		(100 * HZ / 1000)
 
-#endif /* _SCHED_RT_H */
+#endif /* _LINUX_SCHED_RT_H */