sched: add declaration of sched_tail to sched.h

Avoids sparse warnings:
kernel/sched.c:2170:17: warning: symbol 'schedule_tail' was not declared. Should it be static?

Avoids the need for an external declaration in arch/um/process.c

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
index fc50d2f..e8cb9ff 100644
--- a/arch/um/kernel/process.c
+++ b/arch/um/kernel/process.c
@@ -128,8 +128,6 @@
 	return current;
 }
 
-extern void schedule_tail(struct task_struct *prev);
-
 /*
  * This is called magically, by its address being stuffed in a jmp_buf
  * and being longjmp-d to.
diff --git a/include/linux/sched.h b/include/linux/sched.h
index e217d18..9c17e82 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -242,6 +242,7 @@
 
 extern void sched_init(void);
 extern void sched_init_smp(void);
+extern asmlinkage void schedule_tail(struct task_struct *prev);
 extern void init_idle(struct task_struct *idle, int cpu);
 extern void init_idle_bootup_task(struct task_struct *idle);