Stop using `to_hir_binop` in codegen This came up in https://github.com/rust-lang/rust/pull/125359#discussion_r1609401311 , and looking into it we can just use the `mir::BinOp`s directly instead of `hir::BinOpKind`s. (AKA rather than going `mir::BinOp` → `hir::BinOpKind` → `IntPredicate`, just go `mir::BinOp` → `IntPredicate`.)
Please read the rustc-dev-guide chapter on Backend Agnostic Codegen.