This is the most simple solution that use:
// Use this as first line upon load of page
$sort = $_GET['s'];
// Then simply sort according to that variable
$sql="SELECT * FROM tracks ORDER BY $sort";
echo '<tr>';
echo '<td><a href="report_tracks.php?s=title">Title</a><td>';
echo '<td><a href="report_tracks.php?s=album">Album</a><td>';
echo '<td><a href="report_tracks.php?s=artist">Artist</a><td>';
echo '<td><a href="report_tracks.php?s=count">Count</a><td>';
echo '</tr>';