2 compile-fail tests' failure modes changed with new lambda syntax

I'm xfailing the following tests: liveness-closure-require-ret, and liveness-issue-2163.

With the new syntax these still fail but with a different error message. Before they failed with 'not all control paths return a value', and now they fail with type errors. @nikomatsakis you might be able to tell whether these are still working as intended.
