sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task.h>

We are going to split <linux/sched/task.h> out of <linux/sched.h>, which
will have to be picked up from other headers and a couple of .c files.

Create a trivial placeholder <linux/sched/task.h> file that just
maps to <linux/sched.h> to make this patch obviously correct and
bisectable.

Include the new header in the files that are going to need it.

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>

mm/kmemleak.c

@@ -74,6 +74,7 @@
 #include <linux/kernel.h>
 #include <linux/list.h>
 #include <linux/sched/signal.h>
+#include <linux/sched/task.h>
 #include <linux/jiffies.h>
 #include <linux/delay.h>
 #include <linux/export.h>

mm/memory-failure.c

@@ -41,6 +41,7 @@
 #include <linux/page-flags.h>
 #include <linux/kernel-page-flags.h>
 #include <linux/sched/signal.h>
+#include <linux/sched/task.h>
 #include <linux/ksm.h>
 #include <linux/rmap.h>
 #include <linux/export.h>

mm/memory.c

@@ -43,6 +43,7 @@
 #include <linux/sched/mm.h>
 #include <linux/sched/coredump.h>
 #include <linux/sched/numa_balancing.h>
+#include <linux/sched/task.h>
 #include <linux/hugetlb.h>
 #include <linux/mman.h>
 #include <linux/swap.h>

mm/oom_kill.c

@@ -24,6 +24,7 @@
 #include <linux/sched.h>
 #include <linux/sched/mm.h>
 #include <linux/sched/coredump.h>
+#include <linux/sched/task.h>
 #include <linux/swap.h>
 #include <linux/timex.h>
 #include <linux/jiffies.h>

mm/rmap.c

@@ -47,6 +47,7 @@
 
 #include <linux/mm.h>
 #include <linux/sched/mm.h>
+#include <linux/sched/task.h>
 #include <linux/pagemap.h>
 #include <linux/swap.h>
 #include <linux/swapops.h>

mm/swapfile.c

@@ -7,6 +7,7 @@
 
 #include <linux/mm.h>
 #include <linux/sched/mm.h>
+#include <linux/sched/task.h>
 #include <linux/hugetlb.h>
 #include <linux/mman.h>
 #include <linux/slab.h>

mm/usercopy.c

@@ -17,6 +17,8 @@
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/sched.h>
+#include <linux/sched/task.h>
+#include <linux/sched/task_stack.h>
 #include <asm/sections.h>
 
 enum {