frobtads: Fix building with current clang

packages/frobtads/tads3-vmtz.cpp.patch

@@ -0,0 +1,14 @@
+https://svnweb.freebsd.org/ports/head/games/frobtads/files/patch-tads3_vmtz.cpp?revision=432973&view=markup
+
+diff -u -r ../frobtads-1.2.3/tads3/vmtz.cpp ./tads3/vmtz.cpp
+--- ../frobtads-1.2.3/tads3/vmtz.cpp	2013-05-17 21:46:51.000000000 +0200
++++ ./tads3/vmtz.cpp	2017-06-12 00:31:09.635744304 +0200
+@@ -1984,7 +1984,7 @@
+              *   the transition in terms of the local time that was in effect
+              *   up until that moment
+              */
+-            result->set(tcur > 0 ? tcur - 1 : tcur);
++            result->set(cur > 0 ? tcur - 1 : tcur);
+             return;
+         }
+     }