[PATCH] uml: readd forgot prototype

This was forgot in a previous patch so UML does not compile with TT mode
enabled.
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/um/include/os.h

@@ -201,6 +201,7 @@ extern int os_getpgrp(void);
 
 #ifdef UML_CONFIG_MODE_TT
 extern void init_new_thread_stack(void *sig_stack, void (*usr1_handler)(int));
+extern void stop(void);
 #endif
 extern void init_new_thread_signals(void);
 extern int run_kernel_thread(int (*fn)(void *), void *arg, void **jmp_ptr);