This includes initial support for the (hopefully final) updated Objective-C ABI, developed here:
https://github.com/davidchisnall/clang-gnustep-abi-2
It also includes some cleanups and refactoring from older GNU ABIs.
This is not yet in a state that's ready to commit (for example, it's currently ELF-only, but doesn't include driver changes to downgrade to the 1.x ABI for non-ELF targets until other binary formats are supported), but it's probably in a state where it could benefit from review.