[Issue 9181] Forward reference error in struct static fields

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=9181

--- Comment #1 from Basile-z <b2.temp at gmx.com> ---
Funnily this alternative, which still needs inference for the array, works

---
struct Foo {
    static immutable foos1 = [F];
    static immutable F = Foo();
} 
---

Because type semantic of `F` is launched when doing the one of `foo1`, hence
`F` is not already "inuse".

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