reverted:
--- b/core/composer.json
+++ a/core/composer.json
@@ -180,8 +180,7 @@
             "lib/Drupal/Core/DrupalKernel.php",
             "lib/Drupal/Core/DrupalKernelInterface.php",
             "lib/Drupal/Core/Site/Settings.php"
+        ]
-        ],
-        "files": ["lib/autoloader.php"]
     },
     "config": {
         "preferred-install": "dist",
reverted:
--- b/core/install.php
+++ a/core/install.php
@@ -21,6 +21,15 @@
  */
 define('MAINTENANCE_MODE', 'install');
 
+// Exit early if running an incompatible PHP version to avoid fatal errors.
+// The minimum version is specified explicitly, as DRUPAL_MINIMUM_PHP is not
+// yet available. It is defined in bootstrap.inc, but it is not possible to
+// load that file yet as it would cause a fatal error on older versions of PHP.
+if (version_compare(PHP_VERSION, '7.0.8') < 0) {
+  print 'Your PHP installation is too old. Drupal requires at least PHP 7.0.8. See the <a href="https://www.drupal.org/requirements">system requirements</a> page for more information.';
+  exit;
+}
+
 // Initialize the autoloader.
 $class_loader = require_once $root_path . '/autoload.php';
 
reverted:
--- b/core/lib/autoloader.php
+++ /dev/null
@@ -1,14 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains on autoload include event related functionality.
- */
-
-use Drupal\Core\Requirements;
-
-// Checking minimum PHP version to avoid fatal errors.
-if (defined('MAINTENANCE_MODE') && MAINTENANCE_MODE === 'install' && version_compare(PHP_VERSION, Requirements::MINIMUM_PHP) < 0) {
-  print 'Your PHP installation is too old. Drupal requires at least PHP ' . Requirements::MINIMUM_PHP . '. See the <a href="https://www.drupal.org/requirements">system requirements</a> page for more information.';
-  exit;
-}