set CUDA_VERSION during build; test torch.version.cuda is correct

Author: h-vetinari

recipe/bld.bat

@@ -93,6 +93,7 @@ if not "%cuda_compiler_version%" == "None" (
     set MAGMA_HOME=%LIBRARY_PREFIX%
     set "PATH=%CUDA_BIN_PATH%;%PATH%"
     set CUDNN_INCLUDE_DIR=%LIBRARY_PREFIX%\include
+    set "CUDA_VERSION=%cuda_compiler_version%"
 ) else (
     set USE_CUDA=0
     @REM MKLDNN is an Apache-2.0 licensed library for DNNs and is used

recipe/build.sh

@@ -219,6 +219,7 @@ elif [[ ${cuda_compiler_version} != "None" ]]; then
     export USE_STATIC_CUDNN=0
     export MAGMA_HOME="${PREFIX}"
     export USE_MAGMA=1
+    export CUDA_VERSION=$cuda_compiler_version
     # turn off noisy nvcc warnings
     export CMAKE_CUDA_FLAGS="-w -Xptxas -w"
 else

recipe/meta.yaml

@@ -403,6 +403,7 @@ outputs:
         - python -c "import torch; assert torch.backends.cuda.is_built()"          # [linux64 and (cuda_compiler_version != "None")]
         - python -c "import torch; assert torch.backends.cudnn.is_available()"     # [linux64 and (cuda_compiler_version != "None")]
         - python -c "import torch; assert torch.backends.cudnn.enabled"            # [linux64 and (cuda_compiler_version != "None")]
+        - python -c "import torch; assert torch.version.cuda is not None"           # [cuda_compiler_version != "None"]
         # At conda-forge, we target versions of OSX that are too old for MPS support
         # But if users install a newer version of OSX, they will have MPS support
         # https://github.com/conda-forge/pytorch-cpu-feedstock/pull/123#issuecomment-1186355073