Add kbuild.h that contains common definitions for kbuild users

The same definitions are used for the bounds logic and the asm-offsets.h
generation by kbuild. Put them into include/linux/kbuild.h file.

Also add a new feature

COMMENT("text")

which can be used to insert lines of ocmments into asm-offsets.h and
bounds.h.

Cc: Sam Ravnborg <[e-mail]>
Signed-off-by: Christoph Lameter <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Ralf Baechle <[e-mail]>
Cc: Jay Estabrook <[e-mail]>
Cc: Ivan Kokshaysky <[e-mail]>
Cc: Richard Henderson <[e-mail]>
Cc: "Luck, Tony" <[e-mail]>
Cc: Russell King <[e-mail]>
Cc: Chris Zankel <[e-mail]>
Cc: David S. Miller <[e-mail]>
Cc: Haavard Skinnemoen <[e-mail]>
Cc: Bryan Wu <[e-mail]>
Cc: Mike Frysinger <[e-mail]>
Cc: Yoshinori Sato <[e-mail]>
Cc: Geert Uytterhoeven <[e-mail]>
Cc: Roman Zippel <[e-mail]>
Cc: Greg Ungerer <[e-mail]>
Cc: David Howells <[e-mail]>
Cc: Kyle McMartin <[e-mail]>
Cc: Grant Grundler <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Benjamin Herrenschmidt <[e-mail]>
Cc: Martin Schwidefsky <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Paul Mundt <[e-mail]>
Cc: Miles Bader <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/kbuild.h

···
+#ifndef __LINUX_KBUILD_H
+#define __LINUX_KBUILD_H
+
+#define DEFINE(sym, val) \
+        asm volatile("\n->" #sym " %0 " #val : : "i" (val))
+
+#define BLANK() asm volatile("\n->" : : )
+
+#define OFFSET(sym, str, mem) \
+	DEFINE(sym, offsetof(struct str, mem))
+
+#define COMMENT(x) \
+	asm volatile("\n->#" x)
+
+#endif

kernel/bounds.c

···
 /* Include headers that define the enum constants of interest */
 #include <linux/page-flags.h>
 #include <linux/mmzone.h>
-
-#define DEFINE(sym, val) \
-        asm volatile("\n->" #sym " %0 " #val : : "i" (val))
-
-#define BLANK() asm volatile("\n->" : : )
+#include <linux/kbuild.h>
 
 void foo(void)
 {