[llvm] [ARM]: codegen `llvm.roundeven.v*` (PR #141786)

[Folkert de Vries via llvm-commits]

folkertdev wrote:

Allright, `roundeven` generates `vrintn` now. Are there any other parts of the PR you linked that are important (it's large and from a while ago, and the arm backend is different, so I'm having a hard time figuring out what is relevant and what is not).

https://github.com/llvm/llvm-project/pull/141786