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);
ue='grep'>log msg</option>
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</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=0a99022229996492eecaba16968dad750c05fa65'>root</a>/<a href='/guix/log/d3.v3.js?id=0a99022229996492eecaba16968dad750c05fa65'>d3.v3.js</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/d3.v3.js?id=0a99022229996492eecaba16968dad750c05fa65&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2016-12-14 21:58:32 +0100'>2016-12-14</span></td><td><a href='/guix/commit/d3.v3.js?id=4d93f312f084c34a70cf7da3abe5f92a74d76861'>graph: Add d3js backend.</a><span class='msg-avail'>...<span class='msg-tooltip'>* d3.v3.js, graph.js: New files.
* Makefile.am (EXTRA_DIST): List them.
* guix/graph.scm (%d3js-backend): New variable.
(emit-d3js-prologue, emit-d3js-epilogue, emit-d3js-node,
emit-d3js-edge): New procedures.
(%graph-backends): Add %d3js-backend.
</span></span></td><td>Ricardo Wurmus</td></tr>