Temporarily xfail compile-fail/pattern-tyvar

So that the tinderboxes can go green again. Patrick, please look into
this at some point.

Author: marijnh

src/test/compile-fail/pattern-tyvar.rs

@@ -1,3 +1,6 @@
+// xfail-stage0
+// xfail-stage1
+// xfail-stage2
 // -*- rust -*-
 use std;
 import std::option;