fixes llvm 3.6 build due to recent api changes

See: https://github.com/llvm-mirror/llvm/commit/548f2b6e8fc5499fa8c9394fe7d110f50c487802
I don't know,  as far as I could tell reading the diff / compile error message origerrorobj is now a `ErrorOr<std::unique_ptr<ObjectFile>>`, so the above should be correct.