foo.php

<?php
// in POST_AUTOLOAD_DUMP

$map = include('autoload_classmap.php');
// TODO lowercase all keys
file_put_contents('autoload_classmap_insentitive.php', '<?php return '.var_export($map, 1));

// at RUNTIME
require 'vendor/autoload.php';

spl_autoload_register(function ($class) {
    $map = include('autoload_classmap_insentitive.php');
  
    if (isset($map[$class = strtolower($class)])) {
        require $map[$class];
    }
});