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

[Fangrui Song via llvm-commits]

MaskRay wrote:

> Sorry are you sure this is true? I just double checked:

I am sure. The clang behavior looks reasonable. The executable `clang` and headers are separate. Clang headers are only useful for projects that use Clang API. Similarly, lld headers are often unneeded.

Can you clarify things in the PR description? State the behavior of `lld;lld-headers;lld-libraries` respectively when they are used in LLVM_DISTRIBUTION_COMPONENTS.

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