lib/list_sort.c: rearrange includes

Memory allocation only happens in the self test, just as random numbers
are only used there. So move the inclusion of slab.h inside the
CONFIG_TEST_LIST_SORT.

We don't need module.h and all of the stuff it carries with it, so replace
with export.h and compiler.h. Unfortunately, the ARRAY_SIZE macro from
kernel.h requires the user to ensure bug.h is also included (for
BUILD_BUG_ON_ZERO, used by __must_be_array). We used to get that through
some maze of nested includes, but just include it explicitly.

linux/string.h is then only included implicitly through
kernel.h->printk.h->dynamic_debug.h, but only if !CONFIG_DYNAMIC_DEBUG, so
just include it explicitly (for memset).

objdump -d says the generated code is the same, and wc -l says that
lib/.list_sort.o.cmd went from 579 to 165 lines.

Signed-off-by: Rasmus Villemoes <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

lib/list_sort.c

···
 #define pr_fmt(fmt) "list_sort_test: " fmt
 
 #include <linux/kernel.h>
-#include <linux/module.h>
+#include <linux/bug.h>
+#include <linux/compiler.h>
+#include <linux/export.h>
+#include <linux/string.h>
 #include <linux/list_sort.h>
-#include <linux/slab.h>
 #include <linux/list.h>
 
 #define MAX_LIST_LENGTH_BITS 20
···
 
 #ifdef CONFIG_TEST_LIST_SORT
 
+#include <linux/slab.h>
 #include <linux/random.h>
 
 /*