sched: declare pid_alive as inline

We accidentally declared pid_alive without any extern/inline connotation.
Some platforms were fine with this, some like ia64 and mips were very angry.
If the function is inline, the prototype should be inline!

on ia64:
include/linux/sched.h:1718: warning: 'pid_alive' declared inline after
being called
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>

include/linux/sched.h

@@ -1561,7 +1561,7 @@ static inline pid_t task_tgid_vnr(struct task_struct *tsk)
 }
 
 
-static int pid_alive(const struct task_struct *p);
+static inline int pid_alive(const struct task_struct *p);
 static inline pid_t task_ppid_nr_ns(const struct task_struct *tsk, struct pid_namespace *ns)
 {
 	pid_t pid = 0;