use value of DIRECTORY_SEPARATOR to detect Windows

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

Author: xabbuh

Iterator/PathFilterIterator.php

@@ -28,7 +28,7 @@ public function accept()
     {
         $filename = $this->current()->getRelativePathname();
 
-        if (defined('PHP_WINDOWS_VERSION_MAJOR')) {
+        if ('\\' === DIRECTORY_SEPARATOR) {
             $filename = strtr($filename, '\\', '/');
         }
 

Tests/FinderTest.php

@@ -734,7 +734,7 @@ public function getTestPathData()
      */
     public function testAccessDeniedException(Adapter\AdapterInterface $adapter)
     {
-        if (defined('PHP_WINDOWS_VERSION_MAJOR')) {
+        if ('\\' === DIRECTORY_SEPARATOR) {
             $this->markTestSkipped('chmod is not supported on Windows');
         }
 
@@ -773,7 +773,7 @@ public function testAccessDeniedException(Adapter\AdapterInterface $adapter)
      */
     public function testIgnoredAccessDeniedException(Adapter\AdapterInterface $adapter)
     {
-        if (defined('PHP_WINDOWS_VERSION_MAJOR')) {
+        if ('\\' === DIRECTORY_SEPARATOR) {
             $this->markTestSkipped('chmod is not supported on Windows');
         }