XFAIL run-fail/linked-failure

This test is hitting a bug in the runtime that makes it fail incorrectly and
not valgrind-clean

src/test/run-fail/linked-failure.rs

@@ -1,6 +1,7 @@
 // -*- rust -*-
 
 // error-pattern:1 == 2
+// xfail-test
 // no-valgrind
 use std;
 import std::task;