Encode dwarf slot dies for dynamic-sized slots (or slots in dynamic-sized frames)

[graydon]

Currently the presence of a single type-parameter in a frame causes slot offset calculations to go out the window (for locals, not for types). There is enough machinery in dwarf.ml to fix this now. Do so.

[graydon]

Encode and decode tag types in dwarf properly. Add list module to std. Shift rustc to use std.util.option. Fix various dependent bugs. Closed by 57c7e94.