machinst x64: fix checked div sequence

- it should mark as clobbering (def) rdx, not modifying it
- the signed-div check requires a temporary to compare against int64_min

cranelift/codegen/src/isa/x64/inst/args.rs

@@ -199,7 +199,7 @@ impl RegMemImm {
         match self {
             Self::Reg { reg } => collector.add_use(*reg),
             Self::Mem { addr } => addr.get_regs_as_uses(collector),
-            Self::Imm { simm32: _ } => {}
+            Self::Imm { .. } => {}
         }
     }
 }