Skip the phar building on HHVM

Building a phar does not work on HHVM. It looks like it tries to read the phar file which does not exist yet.

tests/Composer/Test/AllFunctionalTest.php

@@ -60,6 +60,10 @@ class AllFunctionalTest extends \PHPUnit_Framework_TestCase
 
     public function testBuildPhar()
     {
+        if (defined('HHVM_VERSION')) {
+            $this->markTestSkipped('Building the phar does not work on HHVM.');
+        }
+        
         $fs = new Filesystem;
         $fs->removeDirectory(dirname(self::$pharPath));
         $fs->ensureDirectoryExists(dirname(self::$pharPath));