Hide __atexit and __atexit_register_cleanup()

Wrap __cxa_{atexit,finalize}() so the call from exit() goes direct
Switch regress/lib/libc/atexit/ to be built with -static so that it can
still access __atexit*
ok millert@ jca@

src/lib/libc/stdlib/atexit.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: atexit.c,v 1.21 2015/04/07 01:27:07 guenther Exp $ */
+/*	$OpenBSD: atexit.c,v 1.22 2015/10/25 18:01:24 guenther Exp $ */
 /*
  * Copyright (c) 2002 Daniel Hartmeier
  * All rights reserved.
@@ -103,6 +103,7 @@ unlock:
 	_ATEXIT_UNLOCK();
 	return (ret);
 }
+DEF_STRONG(__cxa_atexit);
 
 /*
  * Call all handlers registered with __cxa_atexit() for the shared
@@ -180,6 +181,7 @@ restart:
 
 	}
 }
+DEF_STRONG(__cxa_finalize);
 
 /*
  * Register the cleanup function

src/lib/libc/stdlib/atexit.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: atexit.h,v 1.9 2014/06/18 19:01:10 kettenis Exp $ */
+/*	$OpenBSD: atexit.h,v 1.10 2015/10/25 18:01:24 guenther Exp $ */
 
 /*
  * Copyright (c) 2002 Daniel Hartmeier
@@ -41,7 +41,12 @@ struct atexit {
 	} fns[1];			/* the table itself */
 };
 
+__BEGIN_HIDDEN_DECLS
 extern struct atexit *__atexit;		/* points to head of LIFO stack */
+__END_HIDDEN_DECLS
 
 int	__cxa_atexit(void (*)(void *), void *, void *);
 void	__cxa_finalize(void *);
+
+PROTO_NORMAL(__cxa_atexit);
+PROTO_NORMAL(__cxa_finalize);