[TIPC]: Fix headercheck wrt. tipc_config.h

It wants string functions like memcpy() for inline
routines, and these define userland interfaces.

The only clean way to deal with this is to simply
put linux/string.h into unifdef-y and have it
include <string.h> when not-__KERNEL__.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/Kbuild

@@ -326,6 +326,7 @@ unifdef-y += sonypi.h
 unifdef-y += soundcard.h
 unifdef-y += stat.h
 unifdef-y += stddef.h
+unifdef-y += string.h
 unifdef-y += synclink.h
 unifdef-y += sysctl.h
 unifdef-y += tcp.h

include/linux/string.h

@@ -3,16 +3,14 @@
 
 /* We don't want strings.h stuff being user by user stuff by accident */
 
-#ifdef __KERNEL__
+#ifndef __KERNEL__
+#include <string.h>
+#else
 
 #include <linux/compiler.h>	/* for inline */
 #include <linux/types.h>	/* for size_t */
 #include <linux/stddef.h>	/* for NULL */
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 extern char *strndup_user(const char __user *, long);
 
 /*
@@ -111,9 +109,5 @@ extern void *kmemdup(const void *src, size_t len, gfp_t gfp);
 extern char **argv_split(gfp_t gfp, const char *str, int *argcp);
 extern void argv_free(char **argv);
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif
 #endif /* _LINUX_STRING_H_ */