See https://bugs.freedesktop.org/show_bug.cgi?id=47792;
should become obsolete with the next release.

diff -u luit-1.1.1.orig/sys.c luit-1.1.1/sys.c
--- luit-1.1.1.orig/sys.c	2012-03-23 05:23:07.000000000 +0100
+++ luit-1.1.1/sys.c	2013-11-27 22:45:53.000000000 +0100
@@ -20,6 +20,8 @@
 THE SOFTWARE.
 */
 
+#define _XOPEN_SOURCE 600
+
 #ifdef HAVE_CONFIG_H
 # include "config.h"
 #endif
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<tr><td><span title='2022-03-09 23:38:18 +0100'>2022-03-09</span></td><td><a href='/guix/commit/gnu/packages/hurd.scm?id=a9a64c19830ac0fc92bf9eac5d83751df683ff31'>gnu: hurd: Adjust to the transition from "--system" to "gnu.system".</a><span class='msg-avail'>...<span class='msg-tooltip'>This is a followup to 0dc019e19a23fea614be5623360849ab9bc35e74, which
inadvertently led the Hurd to fail to boot.

* gnu/packages/hurd.scm (hurd)[arguments]: In 'create-runsystem' phase,
expect "gnu.system=" instead of "--system=".
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-02-15 22:43:29 +0100'>2022-02-15</span></td><td><a href='/guix/commit/gnu/packages/hurd.scm?id=6ec07f6b38f8839f837590823f181a37b016c6b0'>gnu: hurd: Remove leftover export.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/hurd.scm: Remove 'hurd-triplet?' export.
</span></span></td><td>Jan (janneke) Nieuwenhuizen</td></tr>