swift234

Emit a -dealloc method for Swift classes whose root class is defined in Objective-C.

Teach SILGen to emit a -dealloc method that runs user code, destroys
instance variables, and then calls up to the superclass dealloc. Teach
IRGen to deal with Objective-C destructor methods and add -dealloc to
the instance method table.

There are a few things still wrong here: we're emitting both a Swift
destructor and -dealloc, even though only one of them should ever
actually be used. Additionally, instance variables shouldn't be
destroyed in -dealloc, but in .cxx_destruct, so they persist until the
last of the -dealloc methods is invoked.

Swift SVN r12115