As pointed out by Richard Guenther our definition

of NULL was incorrect for c++ compilers that aren't
gcc (or pretend to be gcc like clang).
ok miod@

src/include/dirent.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: dirent.h,v 1.21 2011/04/06 11:39:42 miod Exp $	*/
+/*	$OpenBSD: dirent.h,v 1.22 2011/07/03 18:51:01 jsg Exp $	*/
 /*	$NetBSD: dirent.h,v 1.9 1995/03/26 20:13:37 jtc Exp $	*/
 
 /*-
@@ -84,6 +84,8 @@ typedef struct _dirdesc {
 #ifndef NULL
 #ifdef 	__GNUG__
 #define	NULL	__null
+#elif defined(__cplusplus)
+#define	NULL	0L
 #else
 #define	NULL	((void *)0)
 #endif /* __GNUG__ */

src/include/locale.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: locale.h,v 1.7 2011/04/06 11:39:42 miod Exp $	*/
+/*	$OpenBSD: locale.h,v 1.8 2011/07/03 18:51:01 jsg Exp $	*/
 /*	$NetBSD: locale.h,v 1.6 1994/10/26 00:56:02 cgd Exp $	*/
 
 /*
@@ -59,6 +59,8 @@ struct lconv {
 #ifndef NULL
 #ifdef 	__GNUG__
 #define NULL	__null
+#elif defined(__cplusplus)
+#define	NULL	0L
 #else
 #define	NULL	((void *)0)
 #endif

src/include/stddef.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: stddef.h,v 1.11 2011/04/06 11:39:42 miod Exp $	*/
+/*	$OpenBSD: stddef.h,v 1.12 2011/07/03 18:51:01 jsg Exp $	*/
 /*	$NetBSD: stddef.h,v 1.4 1994/10/26 00:56:26 cgd Exp $	*/
 
 /*-
@@ -67,6 +67,8 @@ typedef	__mbstate_t	mbstate_t;
 #ifndef	NULL
 #ifdef 	__GNUG__
 #define NULL	__null
+#elif defined(__cplusplus)
+#define	NULL	0L
 #else
 #define	NULL	((void *)0)
 #endif

src/include/stdio.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: stdio.h,v 1.39 2011/04/06 11:39:42 miod Exp $	*/
+/*	$OpenBSD: stdio.h,v 1.40 2011/07/03 18:51:01 jsg Exp $	*/
 /*	$NetBSD: stdio.h,v 1.18 1996/04/25 18:29:21 jtc Exp $	*/
 
 /*-
@@ -58,6 +58,8 @@ typedef	__off_t	off_t;
 #ifndef NULL
 #ifdef 	__GNUG__
 #define	NULL	__null
+#elif defined(__cplusplus)
+#define	NULL	0L
 #else
 #define	NULL	((void *)0)
 #endif

src/include/stdlib.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: stdlib.h,v 1.48 2011/04/06 11:39:42 miod Exp $	*/
+/*	$OpenBSD: stdlib.h,v 1.49 2011/07/03 18:51:01 jsg Exp $	*/
 /*	$NetBSD: stdlib.h,v 1.25 1995/12/27 21:19:08 jtc Exp $	*/
 
 /*-
@@ -80,6 +80,8 @@ typedef struct {
 #ifndef	NULL
 #ifdef 	__GNUG__
 #define NULL	__null
+#elif defined(__cplusplus)
+#define	NULL	0L
 #else
 #define	NULL	((void *)0)
 #endif

src/include/string.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: string.h,v 1.21 2011/04/06 11:39:42 miod Exp $	*/
+/*	$OpenBSD: string.h,v 1.22 2011/07/03 18:51:01 jsg Exp $	*/
 /*	$NetBSD: string.h,v 1.6 1994/10/26 00:56:30 cgd Exp $	*/
 
 /*-
@@ -46,6 +46,8 @@ typedef	__size_t	size_t;
 #ifndef	NULL
 #ifdef 	__GNUG__
 #define	NULL	__null
+#elif defined(__cplusplus)
+#define	NULL	0L
 #else
 #define	NULL	((void *)0)
 #endif

src/include/time.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: time.h,v 1.19 2011/04/06 11:39:42 miod Exp $	*/
+/*	$OpenBSD: time.h,v 1.20 2011/07/03 18:51:01 jsg Exp $	*/
 /*	$NetBSD: time.h,v 1.9 1994/10/26 00:56:35 cgd Exp $	*/
 
 /*
@@ -47,6 +47,8 @@
 #ifndef	NULL
 #ifdef 	__GNUG__
 #define	NULL	__null
+#elif defined(__cplusplus)
+#define	NULL	0L
 #else
 #define	NULL	((void *)0)
 #endif

src/include/unistd.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: unistd.h,v 1.63 2011/04/06 11:39:42 miod Exp $ */
+/*	$OpenBSD: unistd.h,v 1.64 2011/07/03 18:51:01 jsg Exp $ */
 /*	$NetBSD: unistd.h,v 1.26.4.1 1996/05/28 02:31:51 mrg Exp $	*/
 
 /*-
@@ -58,6 +58,8 @@
 #ifndef NULL
 #ifdef 	__GNUG__
 #define	NULL	__null
+#elif defined(__cplusplus)
+#define	NULL	0L
 #else
 #define	NULL	((void *)0)
 #endif

src/include/wchar.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: wchar.h,v 1.17 2011/06/01 16:39:07 millert Exp $	*/
+/*	$OpenBSD: wchar.h,v 1.18 2011/07/03 18:51:01 jsg Exp $	*/
 /*	$NetBSD: wchar.h,v 1.16 2003/03/07 07:11:35 tshiozak Exp $	*/
 
 /*-
@@ -65,6 +65,8 @@
 #ifndef	NULL
 #ifdef	__GNUG__
 #define	NULL	__null
+#elif defined(__cplusplus)
+#define	NULL	0L
 #else
 #define	NULL	((void *)0)
 #endif