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

[Fangrui Song via llvm-commits]

MaskRay wrote:

Thanks. This makes the feature `lld` stricter. Since we don't have `rg 'REQUIRES.*!lld'` and `rg 'UNSUPPORTED.*lld'` tests, this should be safe. (I still don't have 100% confidence level since runtime tests often expose weird behaviors)

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