Can we have ucent ?

[Basile B.]

For the first time today i had needed the ucent type. Fortunately 
it was only for bit operations so easy to do as a struct, however 
this is two hours lost for a type that's in a curious state 
(rename it shrodinger128 maybe ?).

I think that the feature could be implemented as compiler special 
functions that would be located in druntime (with special case 
for GDC and LDC since the type exists in their respective backend 
if i understand correctly).