fix ksm.h breakage of nommu build

Commit 5ad6468801d28c4d4ac9f48ec19297817c915f6a "ksm: let shared pages
be swappable" breaks the build on m68knommu and I suspect on any nommu:

  In file included from kernel/fork.c:52:
  include/linux/ksm.h:129: warning: 'enum ttu_flags' declared inside parameter list
  include/linux/ksm.h:129: warning: its scope is only this definition or declaration, which is probably not what you want
  include/linux/ksm.h:129: error: parameter 2 ('flags') has incomplete type
  make[1]: *** [kernel/fork.o] Error 1
  make[1]: *** Waiting for unfinished jobs....

Let's fix that with CONFIG_MMU around most of the !CONFIG_KSM declarations.

Reported-by: Steven King <sfking@fdwdc.com>
Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Tested-by: Steven King <sfking@fdwdc.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/ksm.h

@@ -94,12 +94,6 @@ void ksm_migrate_page(struct page *newpage, struct page *oldpage);
 
 #else  /* !CONFIG_KSM */
 
-static inline int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
-		unsigned long end, int advice, unsigned long *vm_flags)
-{
-	return 0;
-}
-
 static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
 {
 	return 0;
@@ -114,6 +108,13 @@ static inline int PageKsm(struct page *page)
 	return 0;
 }
 
+#ifdef CONFIG_MMU
+static inline int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
+		unsigned long end, int advice, unsigned long *vm_flags)
+{
+	return 0;
+}
+
 static inline struct page *ksm_might_need_to_copy(struct page *page,
 			struct vm_area_struct *vma, unsigned long address)
 {
@@ -140,6 +141,7 @@ static inline int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page*,
 static inline void ksm_migrate_page(struct page *newpage, struct page *oldpage)
 {
 }
+#endif /* CONFIG_MMU */
 #endif /* !CONFIG_KSM */
 
 #endif /* __LINUX_KSM_H */