[compiler-rt] Check if LLD is built when checking if lto_supported (PR #92752)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Perhaps we should `lld-available` stricter to mean that we have `lld` in the build directory.

`llvm/utils/lit/lit/llvm/config.py` has some `use_lld` code. Can we reuse it?

https://github.com/llvm/llvm-project/pull/92752