This patch removes the _XOPEN_SOURCE preprocessor directive as it does not seem to be needed.
Setting it removes the definition of strdup, which is used in filter-datatypes.c.

Patch by Roel Janssen <roel@gnu.org>
*** a/src/frontend/filter-datatypes.c	1970-01-01 01:00:00.000000000 +0100
--- b/src/frontend/filter-datatypes.c	2018-04-03 17:39:23.177905592 +0200
***************
*** 18,24 ****
   *  Copyright (C) 2006 Steve Harris for Garlik
   */
  
- #define _XOPEN_SOURCE
  #include <stdlib.h>
  #include <string.h>
  #include <math.h>
--- 18,23 ----
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<tr><td><span title='2023-10-24 18:06:21 +0200'>2023-10-24</span></td><td><a href='/guix/commit/gnu/packages/tor.scm?id=1f6babf0c4932b6978249e618bf6d9ec3566b8be'>gnu: tor: Update to 0.4.8.7.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/tor.scm (tor): Update to 0.4.8.7.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>André Batista</td></tr>
<tr><td><span title='2023-09-18 22:32:20 +0300'>2023-09-18</span></td><td><a href='/guix/commit/gnu/packages/tor.scm?id=a515f8b1d8fbda4ea791762fc3987bd5411de077'>gnu: tor: Update to 0.4.8.6.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/tor.scm (tor): Update to 0.4.8.6.
[source]: Remove patch.
* gnu/packages/patches/tor-remove-defensive-assert.patch: Remove file.
* gnu/local.mk (dist_patch_DATA): Remove it.
</span></span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2023-09-14 16:39:20 +0200'>2023-09-14</span></td><td><a href='/guix/commit/gnu/packages/tor.scm?id=de64e412f3684d54bd2a485920cd3287a551f793'>gnu: tor: Update to 0.4.8.5.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/tor.scm (tor): Update to 0.4.8.5.
* gnu/packages/tor.scm (tor)[arguments]&lt;#:configure-flags&gt;:
Add "--enable-gpl".
* gnu/packages/patches/tor-remove-defensive-assert.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/tor.scm (tor)[source]: Add patch to remove defensive
  assert.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>fanquake</td></tr>
<tr><td><span title='2023-08-16 22:13:41 +0200'>2023-08-16</span></td><td><a href='/guix/commit/gnu/packages/tor.scm?id=f3c5c9418b72fa50d6c11f28e1cb6574083e878e'>gnu: tor: Update to 0.4.7.14.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/tor.scm (tor): Update to 0.4.7.14.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>fanquake</td></tr>
<tr><td><span title='2023-07-02 02:00:07 +0200'>2023-07-02</span></td><td><a href='/guix/commit/gnu/packages/tor.scm?id=3e9915724718948f0d74d83aaac1b3c8061c26d2'>gnu: privoxy: Update to 3.0.34.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/tor.scm (privoxy): Update to 3.0.34.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>