Cannot create a type referencing a local constant

```nim
import cps

proc foo() {.cps: Continuation.} =
  const X = 10
  var x: array[X, int]
```

got:

```
test.nim(3, 14) template/generic instantiation of `cps` from here
test.nim(5, 16) Error: undeclared identifier: 'X'
```

The problem is that Nim did not inline `X` into `array[X, int]`, which is carried over to the environment definition, where `X` doesn't exist.