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

[Fangrui Song via llvm-commits]

MaskRay wrote:

I am still confused.  You mentioned the following in the description

> and then ninja install-distribution one does not get an dist/include/lld folder. This PR fixes that. 

I stated that this is the intended behavior: `lld` in LLVM_DISTRIBUTION_COMPONENTS  should not install `include/lld` headers.

Can you clarify this in the PR description?   Suggested description (please confirm the behavior):

This patch allows `lld-headers` and `lld-libraries` in `LLVM_DISTRIBUTION_COMPONENTS` to specify ......
This is similar to `clang;clang-headers;clang-libraries`. When `clang-libraries` or `lld-libraries` is present, `llvm-libraries` must be present as well.

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