cranelift: Fix implicit pointer argument register use (#5301)

* Fix arg handling to write to VRegs instead of physical regs

* Make is_included_in_clobbers required, and handle Args on x64 and riscv64

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

@@ -2236,6 +2236,13 @@ impl MachInst for Inst {
         }
     }
 
+    fn is_included_in_clobbers(&self) -> bool {
+        match self {
+            &Inst::Args { .. } => false,
+            _ => true,
+        }
+    }
+
     fn is_args(&self) -> bool {
         match self {
             Self::Args { .. } => true,