Forcing XPG5 removes locale_t from <locale.h>. 
This breaks including libintl.h, since gettext is built with locale_t
in view.

Index: src/xitk/main.c
--- src/xitk/main.c.orig
+++ src/xitk/main.c
@@ -20,7 +20,7 @@
  *
  */
 /* required for getsubopt(); the __sun test gives us strncasecmp() on solaris */
-#if !defined(__sun) && ! defined(__FreeBSD__) && ! defined(__NetBSD__) && ! defined(__DragonFly__)
+#if !defined(__sun) && ! defined(__FreeBSD__) && ! defined(__NetBSD__) && ! defined(__DragonFly__) && ! defined(__OpenBSD__)
 #define _XOPEN_SOURCE 500
 #endif
 /* required for strncasecmp() */
