A hack for DW_FORM_ref_addr

[Daniel Berlin]

>
> Since DW_FORM_ref_addr requires it, I don't see there is an easy way
> out. I guess I could only save those used by DW_FORM_ref_addr.
>

Back when this support was implemented the first (or was it the second) 
time, I just had it keep around the last 5 or 10 referenced compilation 
units full of dies in an LRU cache, and just reread non-cached CU's as 
necessary.
I think Daniel planned on doing something similar for the third rewrite.
>
> H.J.