External Libraries: Adopt standard get_temp_dir() in Text_Diff::_getTempDir().

This aims to bring more consistency with the rest of core, and more closely mirrors the similar changes upstream to use `sys_get_temp_dir()`.

The potential `false` return value was not checked by the only caller in `Text_Diff_Engine_shell::diff()`.

Follow-up to [7747], [48464], [49185], [60776].

Props TimoTijhof, apermo, SergeyBiryukov.
Fixes #63711.

git-svn-id: https://develop.svn.wordpress.org/trunk@60777 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-includes/Text/Diff.php

@@ -223,33 +223,10 @@ static function trimNewlines(&$line, $key)
      * @access protected
      *
      * @return string  A directory name which can be used for temp files.
-     *                 Returns false if one could not be found.
      */
     static function _getTempDir()
     {
-        $tmp_locations = array('/tmp', '/var/tmp', 'c:\WUTemp', 'c:\temp',
-                               'c:\windows\temp', 'c:\winnt\temp');
-
-        /* Try PHP's upload_tmp_dir directive. */
-        $tmp = ini_get('upload_tmp_dir');
-
-        /* Otherwise, try to determine the TMPDIR environment variable. */
-        if (!strlen($tmp)) {
-            $tmp = getenv('TMPDIR');
-        }
-
-        /* If we still cannot determine a value, then cycle through a list of
-         * preset possibilities. */
-        while (!strlen($tmp) && count($tmp_locations)) {
-            $tmp_check = array_shift($tmp_locations);
-            if (@is_dir($tmp_check)) {
-                $tmp = $tmp_check;
-            }
-        }
-
-        /* If it is still empty, we have failed, so return false; otherwise
-         * return the directory determined. */
-        return strlen($tmp) ? $tmp : false;
+        return get_temp_dir();
     }
 
     /**