Forcing POSIX 1003.1-2001 removes locale_t from <locale.h>.
This breaks including libintl.h, since gettext is built with locale_t
in view.

Index: src/core/util.c
--- src/core/util.c.orig
+++ src/core/util.c
@@ -23,7 +23,7 @@
  */
 
 #define _GNU_SOURCE
-#define _POSIX_C_SOURCE 200112L /* for fdopen() */
+/* #define _POSIX_C_SOURCE 200112L */ /* for fdopen() */
 
 #include <config.h>
 #include <glib/gi18n-lib.h>
