restore old plan 9 property that when the
last thread exits the main proc, the remaining
program ends up in the background and the
program appears to have exited.
diff --git a/src/libthread/threadimpl.h b/src/libthread/threadimpl.h
index 32afa5f..5cdba60 100644
--- a/src/libthread/threadimpl.h
+++ b/src/libthread/threadimpl.h
@@ -122,3 +122,4 @@
 extern int _runthreadspawn(int*, char*, char**);
 extern void _threadsetupdaemonize(void);
 extern void _threaddodaemonize(char*);
+extern void _threadpexit(void);