Static and const variables can refer to other const variables. But a const
variable cannot refer to a static variable.
Erroneous code example:
```compile_fail,E0013
static X: i32 = 42;
const Y: i32 = X;
```
In this example, `Y` cannot refer to `X` here. To fix this, the value can be
extracted as a const and then used:
```
const A: i32 = 42;
static X: i32 = A;
const Y: i32 = A;
```