Merge: Missing a unboxing when compiling a call to `new NativeArray`

In the following code,

~~~nit
var i
i = 4
var na = new NativeArray[Object](i)
~~~

the declaration type of `i` is `nullable Object`, so the C-type of `i` is `val*` (and not `int`).
Therefore, in the `new NativeArray`, it should be unboxed because the C signature expect a `int`.

Pull-Request: #1365
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>