[llvm] [Coroutines] Create C++ noop coroutine with default function attributes (PR #134878)

[Victor Campos via llvm-commits]

vhscampos wrote:

@efriedma-quic Thanks for the review. Honestly C++ coroutines and their codegen are out of my depth, so if possible I'd like to proceed with a small fix here.

If you believe it's more suitable, I can change the code to add function attributes of pac-ret and bti only, instead of calling `Function::createWithDefaultAttr`.

https://github.com/llvm/llvm-project/pull/134878