Deal with missing exports for hostfs

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
index cd40fdd..c4617ba 100644
--- a/arch/um/include/shared/os.h
+++ b/arch/um/include/shared/os.h
@@ -161,6 +161,9 @@
 			      long *spare_out);
 extern int os_change_dir(char *dir);
 extern int os_fchange_dir(int fd);
+extern unsigned os_major(unsigned long long dev);
+extern unsigned os_minor(unsigned long long dev);
+extern unsigned long long os_makedev(unsigned major, unsigned minor);
 
 /* start_up.c */
 extern void os_early_checks(void);