Forcing XPG3 and POSIX 1003.1-1988 removes locale_t from <locale.h>.
This breaks including libintl.h, since gettext is built with locale_t
in view.

Index: src/interp/lex.c
--- src/interp/lex.c.orig
+++ src/interp/lex.c
@@ -32,11 +32,6 @@
 
 /*#define YYSTYPE PNODE*/
 
-#ifdef __OpenBSD__
-#define _XOPEN_SOURCE
-#define _POSIX_SOURCE
-#endif
-
 #include "llstdlib.h"
 #include "table.h"
 #include "translat.h"
