Fix test failure with glibc 2.36:

  https://savannah.gnu.org/bugs/?62948

Patch taken from upstream:

  https://git.savannah.gnu.org/cgit/libcdio.git/commit/?id=56335fff0f21d294cd0e478d49542a43e9495ed0

diff --git a/test/driver/realpath.c b/test/driver/realpath.c
index 289253e..cd46d62 100644
--- a/test/driver/realpath.c
+++ b/test/driver/realpath.c
@@ -1,5 +1,7 @@
 /* -*- C -*-
-  Copyright (C) 2010-2012, 2015, 2017 Rocky Bernstein <rocky@gnu.org>
+
+  Copyright (C) 2010-2012, 2015, 2017, 2022 Rocky Bernstein
+  <rocky@gnu.org>
 
   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -175,16 +177,17 @@ main(int argc, const char *argv[])
         rc = check_rc(symlink(psz_symlink_file, psz_symlink_file),
                       "symlink", psz_symlink_file);
         if (0 == rc) {
-            cdio_realpath(psz_symlink_file, psz_file_check);
-            if (0 != strncmp(psz_file_check, symlink_file, PATH_MAX)) {
+            char *retvalue = cdio_realpath(psz_symlink_file, psz_file_check);
+            if (0 != retvalue) {
+	      if (0 != strncmp(psz_file_check, symlink_file, PATH_MAX)) {
                 fprintf(stderr, "direct cdio_realpath cycle test failed. %s vs %s\n",
                         psz_file_check, symlink_file);
 		rc = 5;
 		goto err_exit;
+	      }
+	      check_rc(unlink(psz_symlink_file), "unlink", psz_symlink_file);
             }
-            check_rc(unlink(psz_symlink_file), "unlink", psz_symlink_file);
         }
-
     }
 
     check_rc(unlink(psz_orig_file), "unlink", psz_orig_file);
'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=c22c29b0c4821ebe2c66a6c76562a41d33ff8392'>root</a>/<a href='/guix/log/gnu?id=c22c29b0c4821ebe2c66a6c76562a41d33ff8392'>gnu</a>/<a href='/guix/log/gnu/ci.scm?id=c22c29b0c4821ebe2c66a6c76562a41d33ff8392'>ci.scm</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/gnu/ci.scm?id=c22c29b0c4821ebe2c66a6c76562a41d33ff8392&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-04-18 15:59:34 +0200'>2023-04-18</span></td><td><a href='/guix/commit/gnu/ci.scm?id=c8bc58a9e705bb4c37d2c4386d1c6050ab324cb1'>ci: Add 'gdb-minimal' to the "core" package set.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2023-03-09 18:14:25 +0100'>2023-03-09</span></td><td><a href='/guix/commit/gnu/ci.scm?id=768b7705977aa951c36bd37e48956bf91dcc7719'>ci: Update the list of GCC versions for the 'core' subset.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-10-22 01:46:55 +0200'>2022-10-22</span></td><td><a href='/guix/commit/gnu/ci.scm?id=a3619079f95213c4f983e69210ed12b38fd31022'>Remove now unnecessary uses of (guix grafts).</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-10-13 17:28:46 +0200'>2022-10-13</span></td><td><a href='/guix/commit/gnu/ci.scm?id=7c2b09f924788a9ed1b149830a4de4e2920d4618'>ci: Honor the system passed to image-&gt;job.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2022-10-11 16:05:31 +0200'>2022-10-11</span></td><td><a href='/guix/commit/gnu/ci.scm?id=22b9734b67b8f5946e09ed28843a9af26f345945'>Revert "guix system: Remove unused 'read-operating-system' procedure."</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-09-24 14:49:09 +0200'>2022-09-24</span></td><td><a href='/guix/commit/gnu/ci.scm?id=ebe9d660a55629f2506db124b0e016885fc61e5c'>gnu: Add compression module.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2022-08-17 11:29:38 +0200'>2022-08-17</span></td><td><a href='/guix/commit/gnu/ci.scm?id=5bbb9af5d99314a79d7f6535d9a3176c2c10e60b'>ci: Fix the images specification.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>