[lld] lld: Add initial support for GNU LTO format (PR #157175)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> I've wanted a faster replacement of ld.bfd for windows, supporting GCC lto, and this could be it.

This change in itself won't be enough for that, though; LLD has a separate, entirely standalone implementation of the linker for each object/executable file format, so whatever this PR does for the ELF linker, would have to be done in the same way for the COFF linker afterwards.

https://github.com/llvm/llvm-project/pull/157175