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

[Maksim Levental via llvm-commits]

makslevental wrote:

> LLVM_DISTRIBUTION_COMPONENTS=clang;clang-headers;lld installs clang headers. This PR makes lld-headers installs lld headers.

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

```bash
(base) mlevental at maksims-MacBook-Pro llvm-project % git rev-parse HEAD
fafbf216156043d1874cb339e44f57bb1e8dd4b6
(base) mlevental at maksims-MacBook-Pro llvm-project % rm -rf build llvm-install-release
(base) mlevental at maksims-MacBook-Pro llvm-project % cmake -B build -S llvm -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS=lld -DLLVM_DISTRIBUTION_COMPONENTS=lld -DCMAKE_INSTALL_PREFIX=llvm-install-release
-- The C compiler identification is AppleClang 16.0.0.16000026
-- The CXX compiler identification is AppleClang 16.0.0.16000026
...
-- Build files have been written to: /Users/mlevental/dev_projects/llvm-project/build
(base) mlevental at maksims-MacBook-Pro llvm-project % cmake --build build --target install-distribution
...
(base) mlevental at maksims-MacBook-Pro llvm-project % ls llvm-install-release
bin
(base) mlevental at maksims-MacBook-Pro llvm-project % ls llvm-install-release/bin
ld.lld		ld64.lld	lld		lld-link	wasm-ld
```


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