Update tools/shlib-compat.

- Update dwarfdump / compiler support.
  Use hex instead of decimal for integers.
  Add boolean and restrict type definitions.
  Add options for specifing dwarfdump and objdump executables.

- Fix reporting missing symbol definitions as matching.

- Compare external variable definitions.

- Exclude special symbols like _init, _end by default.

- Fix test build.
Face the fact that we have no idea where the ports tree really lives.