Work around build failure due to XCB "length" element.
Patch from <https://sources.debian.org/patches/xelb/0.18-4/>.

Author: Martin <debacle@debian.org>
Bug: https://github.com/ch11ng/xelb/issues/28
Bug-Debian: https://bugs.debian.org/1017294

---
--- a/el_client.el
+++ b/el_client.el
@@ -519,7 +519,7 @@
     (`list (xelb-parse-list node))
     (`exprfield (xelb-parse-exprfield node))
     (`switch (xelb-parse-switch node))
-    ((or `comment `doc))                ;simply ignored
+    ((or `comment `doc `length))                ;simply ignored
     (x (error "Unsupported structure content: <%s>" x))))
 
 ;; The car of the result shall be renamed to prevent duplication of slot names
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<div class='path'>path: <a href='/guix/log/?id=d2b7d14db4a1ba454d781f5ea796c4a457aaef02'>root</a>/<a href='/guix/log/po?id=d2b7d14db4a1ba454d781f5ea796c4a457aaef02'>po</a>/<a href='/guix/log/po/packages?id=d2b7d14db4a1ba454d781f5ea796c4a457aaef02'>packages</a>/<a href='/guix/log/po/packages/fi.po?id=d2b7d14db4a1ba454d781f5ea796c4a457aaef02'>fi.po</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/po/packages/fi.po?id=d2b7d14db4a1ba454d781f5ea796c4a457aaef02&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-05-31 17:23:21 +0200'>2023-05-31</span></td><td><a href='/guix/commit/po/packages/fi.po?id=8e9e6a6482f3ba98d1cdcad344ee488e8751fee7'>nls: Update translations.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/guix-cookbook.texi (Top): Mention Slovak.
</span></span></td><td>Florian Pelz</td></tr>
<tr><td><span title='2023-03-07 21:14:57 +0100'>2023-03-07</span></td><td><a href='/guix/commit/po/packages/fi.po?id=d333958763b0840c4cd895601b079b68358a6a46'>nls: Update translations.</a></td><td>Julien Lepiller</td></tr>
<tr><td><span title='2022-12-04 22:25:23 +0100'>2022-12-04</span></td><td><a href='/guix/commit/po/packages/fi.po?id=2e75b328b6bbdadbffe5b643a4891b5026a0defd'>nls: Update translations.</a><span class='msg-avail'>...<span class='msg-tooltip'>po/packages/vi.po: New file.
po/packages/LINGUAS: Add it.
</span></span></td><td>Julien Lepiller</td></tr>
<tr><td><span title='2022-11-04 10:56:38 +0100'>2022-11-04</span></td><td><a href='/guix/commit/po/packages/fi.po?id=a65ce9dd500460af4f97e7398fb35dd817f4c677'>nls: Update translations.</a><span class='msg-avail'>...<span class='msg-tooltip'>* po/guix/lt.po: New file.
* po/guix/LINGUAS: Add lt.
</span></span></td><td>Julien Lepiller</td></tr>
<tr><td><span title='2022-10-06 08:20:20 +0200'>2022-10-06</span></td><td><a href='/guix/commit/po/packages/fi.po?id=70fc8f6d619ce9f16a8cc0bbb10a011bd3a9997a'>nls: Update translations.</a></td><td>Julien Lepiller</td></tr>
<tr><td><span title='2022-09-04 16:52:02 +0200'>2022-09-04</span></td><td><a href='/guix/commit/po/packages/fi.po?id=77e3042aef6d8e519d016555464e466399318b4f'>nls: Update translations.</a></td><td>Julien Lepiller</td></tr>
<tr><td><span title='2022-08-10 23:32:24 +0200'>2022-08-10</span></td><td><a href='/guix/commit/po/packages/fi.po?id=aacbe59fbceb8a93ecb68fed8581dfdd70dafc11'>nls: Update translations.</a><span class='msg-avail'>...<span class='msg-tooltip'>po/guix/bn.po: New file.
po/guix/LINGUAS: Add it.
</span></span></td><td>Julien Lepiller</td></tr>
<tr><td><span title='2022-07-09 21:49:34 +0200'>2022-07-09</span></td><td><a href='/guix/commit/po/packages/fi.po?id=e0d47d8facafb6d6c04741bbf30eefbc68aaefb9'>nls: Update translations.</a><span class='msg-avail'>...<span class='msg-tooltip'>po/guix/tr.po: New file.
po/guix/LINGUAS: Add it.
</span></span></td><td>Julien Lepiller</td></tr>
<tr><td><span title='2022-06-04 17:42:54 +0200'>2022-06-04</span></td><td><a href='/guix/commit/po/packages/fi.po?id=809c57c872a6dd48007d1abf6d7f3dd1482ec53a'>nls: Update translations.</a><span class='msg-avail'>...<span class='msg-tooltip'>po/packages/tr.po: New file.
po/packages/LINGUAS: Add it.
</span></span></td><td>Julien Lepiller</td></tr>
<tr><td><span title='2022-05-01 18:07:34 +0200'>2022-05-01</span></td><td><a href='/guix/commit/po/packages/fi.po?id=6b4124cdcc203d47dc40158062afa1497d73d592'>nls: Update translations.</a><span class='msg-avail'>...<span class='msg-tooltip'>po/guix/ja.po: New file.
po/guix/LINGUAS: Add it.
</span></span></td><td>Julien Lepiller</td></tr>
<tr><td><span title='2022-04-02 18:42:36 +0200'>2022-04-02</span></td><td><a href='/guix/commit/po/packages/fi.po?id=8a208df17fe81fbf34f5a86cc52bb0b8e33c7b96'>nls: Update translations.</a><span class='msg-avail'>...<span class='msg-tooltip'>* po/packages/fi.po: New file.
* po/packages/LINGUAS: Add it.
</span></span></td><td>Julien Lepiller</td></tr>