deskutils/sliderule: include errno.h for errno

errno must be accessed by a macro from errno.h.

PR:		281785
Approved by:	portmgr (build fix blanket), mikael

deskutils/sliderule/Makefile

@@ -1,6 +1,6 @@
 PORTNAME=	sliderule
 PORTVERSION=	1.0
-PORTREVISION=	11
+PORTREVISION=	12
 CATEGORIES=	deskutils
 MASTER_SITES=	LOCAL/joerg
 DISTNAME=	${PORTNAME}

deskutils/sliderule/files/patch-xcalc.c

@@ -0,0 +1,19 @@
+--- xcalc.c.orig
++++ xcalc.c
+@@ -32,6 +32,7 @@
+  *                  it's an option.
+  */
+ 
++#include <errno.h>
+ #include <stdio.h>
+ #include <math.h>
+ #include <signal.h>
+@@ -43,8 +44,6 @@
+ 
+ /* program icon */
+ #include "icon"
+-
+-extern int errno;
+ 
+ 
+ /* constants used for setting up the calculator.  changing them would