Allow Conditional Compilation Inside Enum Declaration

[Timon Gehr]

On 4/2/24 00:00, Paul Backus wrote:
> On Saturday, 30 March 2024 at 14:57:00 UTC, IchorDev wrote:
>> The logical solution is to just allow conditional compilation 
>> statements inside enums:
>> ```d
>> enum A{
>>     x,y,z,
>>     static if(cond){
>>         w,
>>     }
>> }
>> ```
> 
> It's not very elegant, but you can do it with a string mixin:
> 
> ```d
> enum string enumMembers = "x, y, z, " ~ (cond ? "w, " : "");
> 
> mixin("enum A { " ~ enumMembers ~ " }");
> ```

A drawback of this approach is that the enum name is only visible after 
the mixin has been expanded, which can lead to forward reference issues.