More diff.py improvements

[SeekyCt]

• Updated diff.py to the latest version from the original repo again (the update merged the arch_settings and mapfile regex changes this repo had into the main repo, and also added --stop-at-ret support for ppc to end the diff on the first blr found).
• Set up this repo for .o diffing, which allows relocations with symbol names to be included in the diff (to use, run expected.py on an OK build and then use diff.py with -o)
• Set up this repo for automatic rebuilding (run diff.py with the flags -mw and it will rebuild automatically whenever you edit the source code & update the diff, like on decomp.me)
• Set up this repo for showing line numbers in the diff

[SeekyCt]

Apparently matching breaks with -sym on rather than -sym dwarf-2, so I've undone that for now

[SeekyCt]

Fixed line numbers for dwarf-2, so they're back again without breaking anything

[riptl]

@SeekyCt Lgtm, is this ready to merge?

[SeekyCt]

Yeah afaik