Source location info still missing in precompiled code

[shirok]

Precompiled code attaches packed source info, but it seems that it is source code info without location info.
Will come up a short example to exhibit the issue.

[shirok]

Oops. The packed debug info format didn't consider extended pairs.

Extended pairs don't fit nicely with the current packed format, but we can "augument" it with...

• List of offsets of pairs that are extended ant non-empty attributes
• For each of such pairs, packed format of pair attributes

These are applied recursively, e.g. pair attributes may contain extended pairs.

[shirok]

Not necessarily a "list of offsets" to point to extended pairs. We can "flatten" the debug info with extended pairs to an ordinary DAG to encode. We'll reconstruct the original form after decodign the packed form.