merged branch stloyd/bugfix/mimeguesser_functions (PR #6601)

This PR was merged into the 2.0 branch.

Commits
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3195122 [HttpFoundation] Check if required shell functions for `FileBinaryMimeTypeGuesser` are not disabled

Discussion
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[HttpFoundation] Check if required shell functions are not disabled

Rebased to `2.0` & squashed version of #6526.

src/Symfony/Component/HttpFoundation/File/MimeType/FileBinaryMimeTypeGuesser.php

@@ -28,8 +28,9 @@ class FileBinaryMimeTypeGuesser implements MimeTypeGuesserInterface
      */
     public static function isSupported()
     {
-        return !strstr(PHP_OS, 'WIN');
+        return !defined('PHP_WINDOWS_VERSION_BUILD') && function_exists('passthru') && function_exists('escapeshellarg');
     }
+
     /**
      * Guesses the mime type of the file with the given path
      *