JSXv4: Unable to use argument with default value in other default arguments

### Repro

```ml
@react.component
let make = (~a=2, ~b=a*2) => <div />
```

causes the error:

```none
[E] Line 2, column 21:
This has type: option<'a>
  Somewhere wanted: int
```

This used to work with JSXv3.