x/debug: viewcore can't type some stack variables

[mknyszek]

Some stack variables in viewcore and gocore are ignored because gocore doesn't handle them properly. I don't fully understand this yet, but @thanm made us aware of this issue and helpfully left a comment in the code:

"Instead what the code above should be doing is caching any abstract variables it encounters in a map (indexed by DWARF offset), then when it encounters a concrete var, pick the name and type up from the abstract variable."

Than also linked to a design doc for this with examples: https://github.com/golang/proposal/blob/master/design/22080-dwarf-inlining.md#how-the-generated-dwarf-should-look.

[mknyszek]

CC @aktau