swift234

Invalidate the deserializer caches after each SIL linking pass.
This avoids that the deserializer(s) keep references to deserialized functions during the whole optimization passes
(especially dead function elimination).

I have seen no negative effect on compiletime. It seems to be a seldom event that a function is
deserialized twice because of not keeping the cache alive between linking passes.

I also simplified the final dead function elimination by just using the regular dead function elimination pass.




Swift SVN r22837