swift234

Tweak some -parse-stdlib tests

While making some changes that resulted in materializeForSet getting
synthesized more often, I noticed that some tests started failing
because they could not find the Optional type, which appears in the
type of materializeForSet. Fix these tests by defining an Optional
and passing in '-module-name Swift' so that we can find it.

This feels a little bit gross, but Dmitri says it is preferrable to
importing Swift from a test.