I’m trying to build pytorch on Arch Linux with OpenBLAS.  I’m encountering errors about NVCC not being able to find the CUB include files:
[3861/5000] Building NVCC (Device) object caffe2/CMakeFiles/torch_cuda.dir/operators/torch_cuda_generated_affine_channel_op.cu.o
FAILED: caffe2/CMakeFiles/torch_cuda.dir/operators/torch_cuda_generated_affine_channel_op.cu.o 
cd /home/richard/workspace/third_party/pytorch/build/caffe2/CMakeFiles/torch_cuda.dir/operators && /usr/bin/cmake -E make_directory /home/richard/workspace/third_party/pytorch/build/caffe2/CMakeFiles/torch_cuda.dir/operators/. && /usr/bin/cmake -D verbose:BOOL=OFF -D build_configuration:STRING=Release -D generated_file:STRING=/home/richard/workspace/third_party/pytorch/build/caffe2/CMakeFiles/torch_cuda.dir/operators/./torch_cuda_generated_affine_channel_op.cu.o -D generated_cubin_file:STRING=/home/richard/workspace/third_party/pytorch/build/caffe2/CMakeFiles/torch_cuda.dir/operators/./torch_cuda_generated_affine_channel_op.cu.o.cubin.txt -P /home/richard/workspace/third_party/pytorch/build/caffe2/CMakeFiles/torch_cuda.dir/operators/torch_cuda_generated_affine_channel_op.cu.o.Release.cmake
/home/richard/workspace/third_party/pytorch/caffe2/operators/affine_channel_op.cu:3:10: fatal error: cub/block/block_reduce.cuh: No such file or directory
 #include <cub/block/block_reduce.cuh>
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
CMake Error at torch_cuda_generated_affine_channel_op.cu.o.Release.cmake:221 (message):
  Error generating
  /home/richard/workspace/third_party/pytorch/build/caffe2/CMakeFiles/torch_cuda.dir/operators/./torch_cuda_generated_affine_channel_op.cu.o


And more errors of this sort from the build/caffe2/CMakeFiles/torch_cuda.dir/operators directory.  This occurs both on master and on 1.6.0.  I can see the needed file is present at third_party/cub/cub/block/block_reduce.cuh.  My build command is:
CUDA_HOME=/opt/cuda-10.1 CC=/usr/bin/gcc-8 CXX=$(which c++-8)  CMAKE_PREFIX_PATH=~/.local/lib/python3.8 BLAS=OpenBLAS python setup.py build