x64: port some atomics to ISLE (#4212)

* x64: port `fence` to ISLE
* x64: port `atomic_load` to ISLE
* x64: port `atomic_store` to ISLE

cranelift/codegen/src/machinst/isle.rs

@@ -300,6 +300,11 @@ macro_rules! isle_prelude_methods {
             }
         }
 
+        #[inline]
+        fn ty_int(&mut self, ty: Type) -> Option<Type> {
+            ty.is_int().then(|| ty)
+        }
+
         #[inline]
         fn ty_scalar_float(&mut self, ty: Type) -> Option<Type> {
             match ty {