err: Rewrite warnc() and errc() family functions to be standalone

Do not depend on the system vwarn() and verr() functions to implement
the *c() variants, as the system might actually lack any of the <err.h>
BSD extensions.

COPYING

@@ -81,7 +81,7 @@ Files:
  src/fgetln.c
  src/progname.c
 Copyright:
- Copyright © 2005, 2008-2012 Guillem Jover <guillem@hadrons.org>
+ Copyright © 2005, 2008-2012, 2019 Guillem Jover <guillem@hadrons.org>
  Copyright © 2005 Hector Garcia Alvarez
  Copyright © 2005 Aurelien Jarno
  Copyright © 2006 Robert Millan

include/bsd/err.h

@@ -43,15 +43,15 @@
 #include <stdarg.h>
 
 __BEGIN_DECLS
-void warnc(int code, const char *format, ...)
-	__printflike(2, 3);
 void vwarnc(int code, const char *format, va_list ap)
 	__printflike(2, 0);
+void warnc(int code, const char *format, ...)
+	__printflike(2, 3);
 
-void errc(int status, int code, const char *format, ...)
-	__printflike(3, 4) __dead2;
 void verrc(int status, int code, const char *format, va_list ap)
 	__printflike(3, 0) __dead2;
+void errc(int status, int code, const char *format, ...)
+	__printflike(3, 4) __dead2;
 __END_DECLS
 
 #endif

src/err.c

 /*
  * Copyright © 2006 Robert Millan
- * Copyright © 2011 Guillem Jover <guillem@hadrons.org>
+ * Copyright © 2011, 2019 Guillem Jover <guillem@hadrons.org>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -26,8 +26,21 @@
  */
 
 #include <err.h>
-#include <errno.h>
+#include <string.h>
 #include <stdarg.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+void
+vwarnc(int code, const char *format, va_list ap)
+{
+	fprintf(stderr, "%s: ", getprogname());
+	if (format) {
+		vfprintf(stderr, format, ap);
+		fprintf(stderr, ": ");
+	}
+	fprintf(stderr, "%s\n", strerror(code));
+}
 
 void
 warnc(int code, const char *format, ...)
@@ -40,13 +53,15 @@ warnc(int code, const char *format, ...)
 }
 
 void
-vwarnc(int code, const char *format, va_list ap)
+verrc(int status, int code, const char *format, va_list ap)
 {
-	int tmp = errno;
-
-	errno = code;
-	vwarn(format, ap);
-	errno = tmp;
+	fprintf(stderr, "%s: ", getprogname());
+	if (format) {
+		vfprintf(stderr, format, ap);
+		fprintf(stderr, ": ");
+	}
+	fprintf(stderr, "%s\n", strerror(code));
+	exit(status);
 }
 
 void
@@ -58,10 +73,3 @@ errc(int status, int code, const char *format, ...)
 	verrc(status, code, format, ap);
 	va_end(ap);
 }
-
-void
-verrc(int status, int code, const char *format, va_list ap)
-{
-	errno = code;
-	verr(status, format, ap);
-}