swift234

Emit .cxx_destruct for destruction of ivars in Objective-C-derived classes.

The Objective-C runtime executes the .cxx_destruct method after the
last -dealloc has executed when destroying an object, allowing the
instance variables to remain live even after the subclass's
destructor/-dealloc has executed, which is important for memory
safety. This fixes the majority of <rdar://problem/15136592>.

Note that IRGenModule::getAddrOfIVarDestroyer() contains  an egregious
hack to find the ivar destructor SIL function via a linear
search. We need a better way to find SIL functions that we know exist,
because LinkEntity does not suffice.

Swift SVN r12206