swift234

Very initial ARC optimizer implementation.

For simplicity it currently only moves copy_values, strong_retains since we are
not doing the data flow analysis yet.

Even with its limitations (which are extreme), we are removing ~400
retain/release/copyvalue/destroyvalue pairs from the standard library.

Additionally we reduce the time RC4 takes from 7.5-5.5 (2 second delta).

Swift SVN r12264