sched/headers: Split out open-coded prototypes into kernel/sched/smp.h

Move the prototypes for sched_ttwu_pending() and send_call_function_single_ipi()
into the newly created kernel/sched/smp.h header, to make sure they are all
the same, and to architectures happy that use -Wmissing-prototypes.
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/core.c

@@ -20,6 +20,7 @@
 #include "../smpboot.h"
 
 #include "pelt.h"
+#include "smp.h"
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/sched.h>

kernel/sched/smp.h

+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Scheduler internal SMP callback types and methods between the scheduler
+ * and other internal parts of the core kernel:
+ */
+
+extern void sched_ttwu_pending(void *arg);
+
+extern void send_call_function_single_ipi(int cpu);

kernel/smp.c

@@ -22,7 +22,7 @@
 #include <linux/hypervisor.h>
 
 #include "smpboot.h"
-
+#include "sched/smp.h"
 
 #define CSD_TYPE(_csd)	((_csd)->flags & CSD_FLAG_TYPE_MASK)
 
@@ -133,8 +133,6 @@ static __always_inline void csd_unlock(call_single_data_t *csd)
 
 static DEFINE_PER_CPU_SHARED_ALIGNED(call_single_data_t, csd_data);
 
-extern void send_call_function_single_ipi(int cpu);
-
 void __smp_call_single_queue(int cpu, struct llist_node *node)
 {
 	/*
@@ -196,7 +194,6 @@ void generic_smp_call_function_single_interrupt(void)
 	flush_smp_call_function_queue(true);
 }
 
-extern void sched_ttwu_pending(void *);
 extern void irq_work_single(void *);
 
 /**