Do not normalize the kernel root directory path (see symfony/symfony#15474).

src/Symfony/Component/HttpKernel/Kernel.php

@@ -344,7 +344,7 @@ abstract class Kernel implements KernelInterface, TerminableInterface
     {
         if (null === $this->rootDir) {
             $r = new \ReflectionObject($this);
-            $this->rootDir = str_replace('\\', '/', dirname($r->getFileName()));
+            $this->rootDir = dirname($r->getFileName());
         }
 
         return $this->rootDir;