Move werrstr into errstr, so that if you use werrstr

you have to get this __errfmt instead of the one
in libfmt that only does Unix error codes.

src/lib9/errstr.c

@@ -66,3 +66,15 @@ __errfmt(Fmt *f)
 		return fmtstrcpy(f, getsyserr());
 	return fmtstrcpy(f, strerror(errno));
 }
+
+void
+werrstr(char *fmt, ...)
+{
+	va_list arg;
+	char buf[ERRMAX];
+
+	va_start(arg, fmt);
+	vseprint(buf, buf+ERRMAX, fmt, arg);
+	va_end(arg);
+	errstr(buf, ERRMAX);
+}