Allow the compiler to notice "constant" header file.

Both gcc and sparse will speed up tokenization by noticing
when a header file is protected by the standard preprocessor
#ifndef .. #endif exclusion.

However, that requires that the headers actually _use_ that
standard exclusion. Some did their own little broken dance.

include/linux/kobject.h

@@ -12,9 +12,11 @@
  * destructors. 
  */
 
-#if defined(__KERNEL__) && !defined(_KOBJECT_H_)
+#ifndef _KOBJECT_H_
 #define _KOBJECT_H_
 
+#if __KERNEL__
+
 #include <linux/types.h>
 #include <linux/list.h>
 #include <linux/sysfs.h>
@@ -232,5 +234,5 @@ struct subsys_attribute {
 extern int subsys_create_file(struct subsystem * , struct subsys_attribute *);
 extern void subsys_remove_file(struct subsystem * , struct subsys_attribute *);
 
-
+#endif /* __KERNEL__ */
 #endif /* _KOBJECT_H_ */

include/linux/kref.h

@@ -12,9 +12,11 @@
  *
  */
 
-#if defined(__KERNEL__) && !defined(_KREF_H_)
+#ifndef _KREF_H_
 #define _KREF_H_
 
+#if __KERNEL__
+
 #include <linux/types.h>
 #include <asm/atomic.h>
 
@@ -26,4 +28,5 @@ void kref_init(struct kref *kref);
 void kref_get(struct kref *kref);
 void kref_put(struct kref *kref, void (*release) (struct kref *kref));
 
+#endif /* __KERNEL__ */
 #endif /* _KREF_H_ */

include/linux/slab.h

@@ -4,7 +4,7 @@
  * (markhe@nextd.demon.co.uk)
  */
 
-#if	!defined(_LINUX_SLAB_H)
+#ifndef _LINUX_SLAB_H
 #define	_LINUX_SLAB_H
 
 #if	defined(__KERNEL__)