[macppc] mark games/widelands NOT_FOR_ARCHS, colors are partly off

Hi,

Some texture colors are off on powerpc, upstream thinks it's likely
related to the old OpenGL versions or driver used on macppc machines[0].
It's an obvious reminder, but all OpenGL capable macppc machine are
radeon(4) only.

As such i'm proposing to mark it NOT_FOR_ARCHS, this saves 6 bulk
machine hours.

OK?

Charlène.


[0] https://github.com/widelands/widelands/issues/3887


Index: Makefile
===================================================================
RCS file: /cvs/ports/games/widelands/Makefile,v
retrieving revision 1.28
diff -u -p -u -p -r1.28 Makefile
--- Makefile 9 Sep 2019 04:42:10 -0000 1.28
+++ Makefile 1 May 2020 10:44:41 -0000
@@ -1,5 +1,8 @@
# $OpenBSD: Makefile,v 1.28 2019/09/09 04:42:10 rsadowski Exp $

+# See https://github.com/widelands/widelands/issues/3887
+NOT_FOR_ARCHS = powerpc
+
COMMENT= economic and military simulation game

V = 20