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

[David Green via llvm-commits]

davemgreen wrote:

Can you add tests into these files to make sure they are generating correctly in the various configs:
```
llvm/test/CodeGen/ARM/fp16-fullfp16.ll
llvm/test/CodeGen/ARM/fp16-promote.ll
llvm/test/CodeGen/Thumb2/float-intrinsics-double.ll
llvm/test/CodeGen/Thumb2/float-intrinsics-float.ll
```

There are still some oddities on Neon for all the rounding intrinsics, like you mention. I will try and look into those separately but otherwise this looks OK to me.

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