minor #13147 [2.3] for consistency, use value of DIRECTORY_SEPARATOR to detect Windows (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
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[2.3] for consistency, use value of DIRECTORY_SEPARATOR to detect Windows

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

This commit unifies the detection of Windows builds across the Symfony
codebase.

Commits
-------

20a427d use value of DIRECTORY_SEPARATOR to detect Windows

Author: fabpot

Tests/Functional/SecurityRoutingIntegrationTest.php

@@ -30,7 +30,7 @@ public function testRoutingErrorIsNotExposedForProtectedResourceWhenAnonymous($c
      */
     public function testRoutingErrorIsExposedWhenNotProtected($config)
     {
-        if (defined('PHP_WINDOWS_VERSION_BUILD') && PHP_VERSION_ID < 50309) {
+        if ('\\' === DIRECTORY_SEPARATOR && PHP_VERSION_ID < 50309) {
             $this->markTestSkipped('Test hangs on Windows & PHP due to https://bugs.php.net/bug.php?id=60120 fixed in http://svn.php.net/viewvc?view=revision&revision=318366');
         }
 
@@ -46,7 +46,7 @@ public function testRoutingErrorIsExposedWhenNotProtected($config)
      */
     public function testRoutingErrorIsNotExposedForProtectedResourceWhenLoggedInWithInsufficientRights($config)
     {
-        if (defined('PHP_WINDOWS_VERSION_BUILD') && PHP_VERSION_ID < 50309) {
+        if ('\\' === DIRECTORY_SEPARATOR && PHP_VERSION_ID < 50309) {
             $this->markTestSkipped('Test hangs on Windows & PHP due to https://bugs.php.net/bug.php?id=60120 fixed in http://svn.php.net/viewvc?view=revision&revision=318366');
         }