compiler support added for precise GC

[bearophile]

Steven Schveighoffer:

> I also suggest that you look into changing the way structs are allocated  
> if you haven't already.  Right now, they are allocated by creating a new  
> array of size 1.  While this is convenient in terms of avoiding a new  
> function, it means all struct allocations are arrays, and as such will be  
> typed as arrays, with appendable semantics and with GCInfo of an array.

+2

Bye,
bearophile