Ok, are you sure that /usr/local/cuda-8.0 and /usr/local/cuda contain the same CUDA version? I’m pretty sure there’s something wrong with that. All librs are compiled with /usr/local/cuda-8.0 and claim to detect FP16, but not when the extension is compiled.
Another hack would be to add -DCUDA_HAS_FP16=1 here 17.