Add new tool: objdump

We don't provide `objdump` in the tools list (along with `readelf` for example). We do use `objdump` internally to get the disassembly from object files, but we don't provide a way to use the tool for anything else (like inspecting DWARF info).
It's usually possible to use `readelf` to get the same info, but in some cases, it's not. And adding a new tool should be quick.