Code maintenance / verbosity: macros, enums, and casts

[Craig Ringer]

Replying-to-self with some notes/progress on this.

While I'm at it, having started to read more of the systemtap code
properly, it's an absolutely miraculous tool in terms of how easily the
complexity it deals with is hidden from the user. Truly incredible,
thankyou!

TL;DR: WIP patch at https://github.com/ringerc/systemtap-patches . Some
compile issues remain, so it's not even a PoC yet, but I think I've figured
out how it all has to work.

It didn't help that libdw itself, is not exactly ... documented. For anyone
else looking for documention on libdw, elfutils etc, this is one of the few
sources I found:
https://developer.ibm.com/technologies/systems/articles/au-dwarf-debug-format/

(Now that I think I worked much of it out, at some stage I hope I'll be
able to come and add a few comments in relevant places to help explain what
the various visitors do, how the dwarf_query stuff works and which ones
relate to which stap code constructs, etc.)
<https://developer.ibm.com/technologies/systems/articles/au-dwarf-debug-format/>
-- 
 Craig Ringer                   http://www.2ndQuadrant.com/
 2ndQuadrant - PostgreSQL Solutions for the Enterprise