bug #15603 [HttpKernel] Do not normalize the kernel root directory path

#15567 (leofeyer)

This PR was submitted for the 2.7 branch but it was merged into the 2.3 branch instead (closes #15603).

Discussion
----------

[HttpKernel] Do not normalize the kernel root directory path #15567

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #15474
| License       | MIT
| Doc PR        | -

Commits
-------

a53489e Do not normalize the kernel root directory path (see #15474).

src/Symfony/Component/HttpKernel/Kernel.php

@@ -344,7 +344,7 @@ public function getRootDir()
     {
         if (null === $this->rootDir) {
             $r = new \ReflectionObject($this);
-            $this->rootDir = str_replace('\\', '/', dirname($r->getFileName()));
+            $this->rootDir = dirname($r->getFileName());
         }
 
         return $this->rootDir;