[llvm] [DAG] Introduce generic shl_add node [NFC] (PR #88791)

[Philip Reames via llvm-commits]

preames wrote:

> Note - there are a few real clang-format warnings that need cleaning up.

Real ones fixed, remaining failure appears to be a misconfiguration in the bot.

https://github.com/llvm/llvm-project/pull/88791