xnp2: fix the build with ports-gcc

OK bentley@

emulators/xnp2/Makefile

@@ -1,10 +1,10 @@
-# $OpenBSD: Makefile,v 1.14 2019/07/12 20:46:10 sthen Exp $
+# $OpenBSD: Makefile,v 1.15 2019/08/12 17:47:52 cwen Exp $
 
 COMMENT =		PC-9801 emulator
 
 DISTNAME =		xnp2-0.86
 EPOCH =			0
-REVISION =		3
+REVISION =		4
 CATEGORIES =		emulators
 
 HOMEPAGE =		https://www.nonakap.org/np2/

emulators/xnp2/patches/patch-x11_compiler_h

@@ -0,0 +1,25 @@
+$OpenBSD: patch-x11_compiler_h,v 1.1 2019/08/12 17:47:52 cwen Exp $
+
+ports-gcc fix for: 
+error: macro "min" passed 3 arguments, but takes just 2
+From:
+https://github.com/nonakap/xnp2/issues/6
+
+Index: x11/compiler.h
+--- x11/compiler.h.orig
++++ x11/compiler.h
+@@ -117,12 +117,14 @@ typedef	gboolean	BOOL;
+ #define	MAX_PATH	MAXPATHLEN
+ #endif
+ 
++#ifndef __cplusplus
+ #ifndef	max
+ #define	max(a,b)	(((a) > (b)) ? (a) : (b))
+ #endif
+ #ifndef	min
+ #define	min(a,b)	(((a) < (b)) ? (a) : (b))
+ #endif
++#endif /* __cplusplus */
+ 
+ #ifndef	ZeroMemory
+ #define	ZeroMemory(d,n)		memset((d), 0, (n))