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='2020-11-05 16:13:50 +0100'>2020-11-05</span></td><td><a href='/guix/commit/gnu/tests/mail.scm?id=a4e7749e91c5ed9b96117e3bcda8802e8744841e'>services: Remove imports of (ice-9 …) modules.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
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<tr><td><span title='2020-01-20 19:13:17 +0000'>2020-01-20</span></td><td><a href='/guix/commit/gnu/tests/mail.scm?id=b3e28b5ef5e23e564eeac8823ad2c837f7c40650'>tests: mail: Remove %getmail-os from the bottom of the file.</a><span class='msg-avail'>...</span></td><td>Christopher Baines</td></tr>
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<tr><td><span title='2019-05-31 20:22:20 +0100'>2019-05-31</span></td><td><a href='/guix/commit/gnu/tests/mail.scm?id=f6b0e1f8ff6a6459d7d39238ced165f4caa988fe'>services: Add getmail.</a><span class='msg-avail'>...</span></td><td>Christopher Baines</td></tr>
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