So this ends up in llvm-clang right? Have to be careful that it doesn't turn up in normal builds as stuff shits itself when ld.gold is present. But I do want to test this as the default clang linker

Yeah it does, only reason ld.gold and lld don't work out of the box AFAIK is our use of --copy-dt-needed-entries whilst other distros use --no-copy-dt-needed-entries, generally packages will use the system default linker unless they are explicitly looking another linker such as ld.gold e.g. webkit2, also AFAIK. Still would like to test this against other packages that are built with clang I think lld is still too new for packages to look for it explicitly.