lib/string: shrink lib/string.i via IWYU

This diff uses an open source tool include-what-you-use (IWYU) to modify
the include list, changing indirect includes to direct includes. IWYU is
implemented using the IWYUScripts github repository which is a tool that
is currently undergoing development. These changes seek to improve build
times.

This change to lib/string.c resulted in a preprocessed size of
lib/string.i from 26371 lines to 5321 lines (-80%) for the x86
defconfig.

Link: https://github.com/ClangBuiltLinux/IWYUScripts
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Tanzir Hasan <tanzirh@google.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20231226-libstringheader-v6-2-80aa08c7652c@google.com
Signed-off-by: Kees Cook <keescook@chromium.org>

lib/string.c

@@ -15,19 +15,20 @@
  */
 
 #define __NO_FORTIFY
-#include <linux/types.h>
-#include <linux/string.h>
-#include <linux/ctype.h>
-#include <linux/kernel.h>
-#include <linux/export.h>
+#include <linux/bits.h>
 #include <linux/bug.h>
+#include <linux/ctype.h>
 #include <linux/errno.h>
-#include <linux/slab.h>
+#include <linux/limits.h>
+#include <linux/linkage.h>
+#include <linux/stddef.h>
+#include <linux/string.h>
+#include <linux/types.h>
 
+#include <asm/page.h>
+#include <asm/rwonce.h>
 #include <asm/unaligned.h>
-#include <asm/byteorder.h>
 #include <asm/word-at-a-time.h>
-#include <asm/page.h>
 
 #ifndef __HAVE_ARCH_STRNCASECMP
 /**