Why is sort allocating in this case?

[Jack Stouffer via Digitalmars-d-learn]

On Friday, 18 September 2015 at 02:29:55 UTC, Jack Stouffer wrote:
> On Friday, 18 September 2015 at 02:24:44 UTC, Adam D. Ruppe 
> wrote:
>> Works for me. What version are you using? Might be the old one 
>> wasn't actually marked nogc yet.
>
> I'm using the git head, must be a regression.

Well apparently it's not, as I just used digger to check, and the 
digger version of dmd compiles it just fine. I'm not quite sure 
how a mis-build or something like that would manifest itself as a 
@nogc error though.