swift234

Fix a memory leak caused by the ReleaseDevirtualizer.

This occured if a stack-promoted object with a devirtualized final release is not actually allocated on the stack.
Now the ReleaseDevirtualizer models the procedure of a final release more accurately.
It inserts a set_deallocating instruction and calles the deallocator (instead of just the deinit).

This changes also includes two peephole optimizations in IRGen and LLVMStackPromotion which get rid of
unused runtime calls in case the stack promoted object is really allocated on the stack.

This fixes rdar://problem/25068118