pytorch: 0.2.0 → 0.3.1 with CUDA and cuDNN (#38530)

* pytorch-0.3 with optional cuda and cudnn

* pytorch tests reenabled if compiling without cuda

* pytorch: Conditionalize cudnn dependency on cudaSupport

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

* pytorch: Compile with the same GCC version used by CUDA if cudaSupport

Fixes this error:

In file included from /nix/store/gv7w3c71jg627cpcff04yi6kwzpzjyap-cudatoolkit-9.1.85.1/include/host_config.h:50:0,
                 from /nix/store/gv7w3c71jg627cpcff04yi6kwzpzjyap-cudatoolkit-9.1.85.1/include/cuda_runtime.h:78,
                 from <command-line>:0:
/nix/store/gv7w3c71jg627cpcff04yi6kwzpzjyap-cudatoolkit-9.1.85.1/include/crt/host_config.h:121:2: error: #error -- unsupported GNU version! gcc versions later than 6 are not supported!
 #error -- unsupported GNU version! gcc versions later than 6 are not supported!
  ^~~~~

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

* pytorch: Build with joined cudatoolkit

Similar to #30058 for TensorFlow.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

* pytorch: 0.3.0 -> 0.3.1

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

* pytorch: Patch for “refcounted file mapping not supported” failure

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

* pytorch: Skip distributed tests

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

* pytorch: Use the stub libcuda.so from cudatoolkit for running tests

Signed-off-by: Anders Kaseorg <andersk@mit.edu>