Remove 'extern int errno;' from public view in linux/unistd.h

Signed-off-by: David Woodhouse <dwmw2@infradead.org>

include/linux/unistd.h

@@ -1,7 +1,9 @@
 #ifndef _LINUX_UNISTD_H_
 #define _LINUX_UNISTD_H_
 
+#ifdef __KERNEL__
 extern int errno;
+#endif
 
 /*
  * Include machine specific syscallX macros