[llvm] [llvm] Fix GNU/Hurd build (PR #184470)

[Samuel Thibault via llvm-commits]

sthibaul wrote:

> Should do something like
> 
> ```
>   +  SmallString<128> Buf;
>   +  if (!sys::fs::readlink(Path, Buf)) {
>   +    std::string s(Buf.str());
>   +    LibPathCache->insert_link(Path, s);
> ```

Right, it already handles this, done so

https://github.com/llvm/llvm-project/pull/184470