Have threads and processes exit more cleanly whenever possible.

diff --git a/include/thread.h b/include/thread.h
index 88ffd4b..c59aab4 100644
--- a/include/thread.h
+++ b/include/thread.h
@@ -131,6 +131,6 @@
 /* scheduler/sysdeps.c */
 extern int SYSDEPS_SpawnThread( TEB *teb );
 extern void SYSDEPS_SetCurThread( TEB *teb );
-extern void SYSDEPS_ExitThread(void);
+extern void SYSDEPS_ExitThread( int status ) WINE_NORETURN;
 
 #endif  /* __WINE_THREAD_H */