swift234

Turn on +0 self by default.

The only caveat is that:

1. We do not properly recognize when we have a let binding and we
perform a guaranteed dynamic call. In such a case, we add an extra
retain, release pair around the call. In order to get that case I will
need to refactor some code in Callee. I want to make this change, but
not at the expense of getting the rest of this work in.

2. Some of the protocol witness thunks generated have unnecessary
retains or releases in a similar manner.

But this is a good first step.

I am going to send a large follow up email with all of the relevant results, so
I can let the bots chew on this a little bit.

rdar://19933044

Swift SVN r27241