[Bug d/108408] libphobos: Support building on *-*-cygwin

[ibuclaw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108408

ibuclaw at gcc dot gnu.org changed:

           What    |Removed                     |Added
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                 CC|                            |ibuclaw at gcc dot gnu.org

--- Comment #2 from ibuclaw at gcc dot gnu.org ---
(In reply to nightstrike from comment #0)
> +    struct _Bigint {
> +        _Bigint* _next;
> +        int _k;
> +        int _maxwds;
> +        int _sign;
> +        int _wds;
> +        ulong[1] _x;
> +    }
--snip--
> +        _Bigint* _p5s;
> +        int _result_k;
> +        _Bigint* _result;
> +        _Bigint** _freelist;
If some of these definitions are just going to be pointer fields in other
structs, can definitely loose the definition, and just declare an opaque struct
instead (struct _Bigint;)