[lld] [lld] enable installing lld headers as part of distribution (PR #127123)

[Fangrui Song via llvm-commits]

MaskRay wrote:

`lld;lld-headers;lld-libraries;clang;clang-libraries;clang-headers;llvm-libraries` installs `lib/libLLD*` and `lib/libclang*`.
(It seems that llvm-libraries must be present when clang-libraries or lld-libraries is present)

https://github.com/llvm/llvm-project/pull/127123