But maybe, they require you to create special versions of object files where even references internal to each library are referenced there as if they live in a different object file? Is that even possible?
Edit: corrections welcome, but https://github.com/llvm-mirror/lld/tree/master/lib/ReaderWri... seems to indicate that this only sopports Mach-o (and a yaml-based format used for debugging and testing)
The extra information that is needed for an ELF linker (any ELF linker; nothing LLD specific) to operate on functions and global data objects in a fine-grained manner is enabled by -ffunction-sections/-fdata-sections.
For more information, see https://news.ycombinator.com/item?id=13673589