* upstream/master: (42 commits)
  [c10d] No default device for ProcessGroupGloo (pytorch#8888)
  Fix default values for affine= in the docstrings of InstanceNormXd (pytorch#8895)
  Stop making dynamic allocations of PinnedMemoryAllocator. (pytorch#8896)
  [C++ API]  Rework optimization package (pytorch#8815)
  Mention MPICH_MAX_THREAD_SAFETY=multiple. (pytorch#8580)
  Unify isViewable, handle n-dimensional empty tensors. (pytorch#8883)
  Add pos_weight argument to nn.BCEWithLogitsLoss (pytorch#5660) (pytorch#6856)
  [build] Enable clang-specific warnings only when using clang (pytorch#8869)
  Fix cmake cudnn autodetection (pytorch#8891)
  [c10d] Fix link order for building C++ tests (pytorch#8889)
  directly add_subdirectory(nanopb) from torch CMakeLists (pytorch#8870)
  [C++ API] Bag of fixes (pytorch#8843)
  [build] Raise in cmake when seeing NVCC{9/9.1} + GCC6 combo (pytorch#8863)
  Create avg_pool1d in ATen (pytorch#8880)
  throw error when grid_sample is passed unsupported mode (pytorch#8884)
  Allow autograd to work even when the shape of values cannot be determined (pytorch#8641)
  Make at::Tensor::to() const (pytorch#8839)
  [auto] Update onnx to 458c521 - Fix typo (onnx/onnx#1143) onnx/onnx@458c521
  [Caffe2] Fix gradient_check on in-place ops (pytorch#8828)
  Fix as_strided_backward (pytorch#8721)
  ...