Show eventual output of clean sections

This is a hack to investigate why mysqli_insert_packet_overflow.phpt
intermittently fails on AppVeyor, and will be reverted in due time.
See <#5447 (comment)>.

Author: cmb69

run-tests.php

@@ -2497,7 +2497,10 @@ function run_test($php, $file, $env)
                 $clean_params = settings2params($clean_params);
                 $extra = !IS_WINDOWS ?
                     "unset REQUEST_METHOD; unset QUERY_STRING; unset PATH_TRANSLATED; unset SCRIPT_FILENAME; unset REQUEST_METHOD;" : "";
-                system_with_timeout("$extra $php $pass_options $extra_options -q $clean_params $no_file_cache \"$test_clean\"", $env);
+                $clean_output = system_with_timeout("$extra $php $pass_options $extra_options -q $clean_params $no_file_cache \"$test_clean\"", $env);
+                if (trim($clean_output) != '') {
+                    echo "\nCLEAN OUTPUT: $file: $clean_output\n";
+                }
             }
 
             if (!$cfg['keep']['clean']) {