[llvm] [SDag] Notify listeners when deleting a node (PR #66991)

[Craig Topper via llvm-commits]

topperc wrote:

> SelectionDAG::DeleteNode does not notify listeners about node deletion. As a result, SelectionDAG::Legalize may skip legalization of some nodes resulting in "Legalized selection DAG" containing illegal nodes.

Is this because a new node gets allocated in the same memory that `LegalizedNodes` is still pointing at?

https://github.com/llvm/llvm-project/pull/66991