[llvm] VectorUtils: mark lrint, llrint as trivially vectorizable (PR #69945)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

Sorry, I forgot to mention: I have some concerns with the custom RISC-V lowering, that I raised [here](https://github.com/llvm/llvm-project/pull/66924#issuecomment-1740793500), even though Craig approved the patch. I'm worried that I might break [l]lrint on RISC-V by merging this patch: could someone kindly let me know if my concern is real?

https://github.com/llvm/llvm-project/pull/69945