Transpiling loop bodies to functions emits wrong code with aliased variables

Example:

```js
let i;
for(let i in { a:1, b:1 }) {
(function(){ return i; })();
}
```

Generates:
```js
var i;
var loop = function ( i ) {
(function(){ return i$1; })();
};

for(var i$1 in { a:1, b:1 }) loop( i );
```