C bitfields guarantees

[Timon Gehr]

On 7/10/24 03:41, Steven Schveighoffer wrote:
> I stayed away from `extern(C)` specification because I *kinda* see the 
> point that we have no precedent for `extern(C)` to adjust field layout.

Well, it does affect layout:

```d
extern(C) struct S{}
pragma(msg, S.sizeof); // 0LU
pragma(msg, (S[100]).sizeof); // 0LU

struct T{}
pragma(msg, T.sizeof); // 1LU
pragma(msg, (T[100]).sizeof); // 100LU
```

In any case, here, the usage is a bit different, in that the `extern(D)` 
version would just be a bit more restrictive, but still fully compatible.