Why does intpromote spew warnings for ~ operator?

[Steven Schveighoffer]

On 9/12/21 10:14 AM, Steven Schveighoffer wrote:
> With the -preview=intpromote switch, the uncasted negation compiles and 
> runs as expected.

I thought I had tested this, but I must have been wrong. With 
-preview=intpromote, only the `short` version compiles, the `ushort` 
version complains that you can't fit an `int` into a `ushort`.

Which is unfortunate, because most people would not use bitwise negate 
on a `short`, they would do it on a `ushort`.

Still, I feel like D should allow what C allows here (and what currently 
working code expects).

-Steve