32-bit ELF file support

[m4b]

This shouldn't be too much work, as goblin already has all the underlying 32-bit struct support, etc.

Do note however this will have to be resolved, I think: m4b/goblin#86 (comment)

Other than that, the hard part will be removing hardcoded platform relocations in the backends (which will need to be done for arm, other than x86 architecture support, etc.)