https://bugs.gentoo.org/383179

Upstream removed OF macro definition:
https://github.com/yquake2/yquake2/commit/716d72a295c9247b3c88ccd180bb7a517ed99e13

--- a/src/common/unzip/ioapi.h	2018-03-10 20:24:21.000000000 +0300
+++ b/src/common/unzip/ioapi.h	2018-04-10 00:34:08.688675097 +0300
@@ -120,6 +120,9 @@
 #define ZLIB_FILEFUNC_MODE_EXISTING (4)
 #define ZLIB_FILEFUNC_MODE_CREATE   (8)
 
+#ifdef _Z_OF
+#define OF _Z_OF
+#endif
 
 #ifndef ZCALLBACK
  #if (defined(WIN32) || defined(_WIN32) || defined (WINDOWS) || defined (_WINDOWS)) && defined(CALLBACK) && defined (USEWINDOWS_CALLBACK)