Lower BinOp::Cmp to llvm.{s,u}cmp.* intrinsics Lowers `mir::BinOp::Cmp` (`three_way_compare` intrinsic) to the corresponding LLVM `llvm.{s,u}cmp.i8.*` intrinsics. These are the intrinsics mentioned in https://github.com/rust-lang/rust/pull/118310, which are now available in LLVM 19. I couldn't find any follow-up PRs/discussions about this, please let me know if I missed something. r? `@scottmcm`