Non-x86_64 output

[Manouchehri]

Right now x86_64 is hardcoded, we should fetch the arch from Ghidra instead.

[nneonneo]

I think the ABI name only affects relocations, which we're not using anyway since we are generating DWARF data for a finished binary. It might matter if we are generating DWARF for a .o file, but I don't think we really support that anyway.

As far as I can tell, the ABI name doesn't even show up in the output DWARF data in any way. For example, the current ghidra2dwarf works fine for ARM code (after the patch in #21).