Add errc/verrc/warnc/vwarnc family: versions of err/... that take the errno

value to use for the strerror() message as an argument.  Originally from
FreeBSD 3.0
Patch from Steffen Nurpmeso (sdaoden (at) gmail.com) with minor tweaks.

src/include/err.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: err.h,v 1.11 2014/04/21 16:13:24 guenther Exp $	*/
+/*	$OpenBSD: err.h,v 1.12 2014/04/22 00:33:02 guenther Exp $	*/
 /*	$NetBSD: err.h,v 1.11 1994/10/26 00:55:52 cgd Exp $	*/
 
 /*-
@@ -44,6 +44,10 @@ __dead void	err(int, const char *, ...)
 			__attribute__((__format__ (printf, 2, 3)));
 __dead void	verr(int, const char *, __va_list)
 			__attribute__((__format__ (printf, 2, 0)));
+__dead void	errc(int, int, const char *, ...)
+			__attribute__((__format__ (printf, 3, 4)));
+__dead void	verrc(int, int, const char *, __va_list)
+			__attribute__((__format__ (printf, 3, 0)));
 __dead void	errx(int, const char *, ...)
 			__attribute__((__format__ (printf, 2, 3)));
 __dead void	verrx(int, const char *, __va_list)
@@ -52,6 +56,10 @@ void		warn(const char *, ...)
 			__attribute__((__format__ (printf, 1, 2)));
 void		vwarn(const char *, __va_list)
 			__attribute__((__format__ (printf, 1, 0)));
+void		warnc(int, const char *, ...)
+			__attribute__((__format__ (printf, 2, 3)));
+void		vwarnc(int, const char *, __va_list)
+			__attribute__((__format__ (printf, 2, 0)));
 void		warnx(const char *, ...)
 			__attribute__((__format__ (printf, 1, 2)));
 void		vwarnx(const char *, __va_list)
@@ -64,6 +72,10 @@ __dead void	_err(int, const char *, ...)
 			__attribute__((__format__ (printf, 2, 3)));
 __dead void	_verr(int, const char *, __va_list)
 			__attribute__((__format__ (printf, 2, 0)));
+__dead void	_errc(int, int, const char *, ...)
+			__attribute__((__format__ (printf, 3, 4)));
+__dead void	_verrc(int, int, const char *, __va_list)
+			__attribute__((__format__ (printf, 3, 0)));
 __dead void	_errx(int, const char *, ...)
 			__attribute__((__format__ (printf, 2, 3)));
 __dead void	_verrx(int, const char *, __va_list)
@@ -72,6 +84,10 @@ void		_warn(const char *, ...)
 			__attribute__((__format__ (printf, 1, 2)));
 void		_vwarn(const char *, __va_list)
 			__attribute__((__format__ (printf, 1, 0)));
+void		_warnc(int, const char *, ...)
+			__attribute__((__format__ (printf, 2, 3)));
+void		_vwarnc(int, const char *, __va_list)
+			__attribute__((__format__ (printf, 2, 0)));
 void		_warnx(const char *, ...)
 			__attribute__((__format__ (printf, 1, 2)));
 void		_vwarnx(const char *, __va_list)