swift234

Update the zombie function list if we create new functions

Dead function elimination deletes functions making them zombies. A zombie is a
function whose name only exists because debug info might still refer to it.

However, later passes of specialization might create a new function by the same
name again. We now have a zombie function (which is just an alias to a deleted
method stub) and a function definition.

No test case since I could not reduce this to a small test case.

rdar://24659988