Make sure CUDA_VERSION is set for conda-build

[atalman]

Make sure CUDA_VERSION is set for conda-build.
I am observing something like this in latest builds:

2023-07-07T07:11:34.2639532Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:494: UserWarning: The environment variable 'BUILD_SPLIT_CUDA' is undefined.
2023-07-07T07:11:34.2640043Z   warnings.warn(
2023-07-07T07:11:34.2640526Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:494: UserWarning: The environment variable 'CUDA_VERSION' is undefined.
2023-07-07T07:11:34.2640847Z   warnings.warn(
2023-07-07T07:11:34.2641544Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:499: UserWarning: The environment variable 'CUDNN_VERSION' is being passed through with value '8.7.0'.  If you are splitting build and test phases with --no-test, please ensure that this value is also set similarly at test time.
2023-07-07T07:11:34.2642106Z   warnings.warn(
2023-07-07T07:11:34.2642888Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:499: UserWarning: The environment variable 'CONDA_CUDATOOLKIT_CONSTRAINT' is being passed through with value '    - pytorch-cuda >=11.8,<11.9 # [not osx]'.  If you are splitting build and test phases with --no-test, please ensure that this value is also set similarly at test time.
2023-07-07T07:11:34.2643406Z   warnings.warn(
2023-07-07T07:11:34.2644132Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:499: UserWarning: The environment variable 'CONDA_TRITON_CONSTRAINT' is being passed through with value '    - torchtriton==2.1.0+440fd1bf20'.  If you are splitting build and test phases with --no-test, please ensure that this value is also set similarly at test time.
2023-07-07T07:11:34.2644635Z   warnings.warn(
2023-07-07T07:11:34.2645062Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:494: UserWarning: The environment variable 'USE_CUDA' is undefined.
2023-07-07T07:11:34.2645369Z   warnings.warn(
2023-07-07T07:11:34.2646025Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:499: UserWarning: The environment variable 'CMAKE_ARGS' is being passed through with value ''.  If you are splitting build and test phases with --no-test, please ensure that this value is also set similarly at test time.
2023-07-07T07:11:34.2646486Z   warnings.warn(
2023-07-07T07:11:34.2647180Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:499: UserWarning: The environment variable 'EXTRA_CAFFE2_CMAKE_FLAGS' is being passed through with value ''.  If you are splitting build and test phases with --no-test, please ensure that this value is also set similarly at test time.
2023-07-07T07:11:34.2647661Z   warnings.warn(
2023-07-07T07:11:34.2648080Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:494: UserWarning: The environment variable 'DEVELOPER_DIR' is undefined.
2023-07-07T07:11:34.2648398Z   warnings.warn(
2023-07-07T07:11:34.2648814Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:494: UserWarning: The environment variable 'DEBUG' is undefined.
2023-07-07T07:11:34.2649342Z   warnings.warn(
2023-07-07T07:11:34.2650005Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:499: UserWarning: The environment variable 'USE_FBGEMM' is being passed through with value '1'.  If you are splitting build and test phases with --no-test, please ensure that this value is also set similarly at test time.
2023-07-07T07:11:34.2650470Z   warnings.warn(
2023-07-07T07:11:34.2651262Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:499: UserWarning: The environment variable 'USE_GLOO_WITH_OPENSSL' is being passed through with value '1'.  If you are splitting build and test phases with --no-test, please ensure that this value is also set similarly at test time.
2023-07-07T07:11:34.2651736Z   warnings.warn(
2023-07-07T07:11:34.2652161Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:494: UserWarning: The environment variable 'USE_DISTRIBUTED' is undefined.
2023-07-07T07:11:34.2652487Z   warnings.warn(
2023-07-07T07:11:34.2652943Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:494: UserWarning: The environment variable 'CMAKE_OSX_ARCHITECTURES' is undefined.
2023-07-07T07:11:34.2653262Z   warnings.warn(
2023-07-07T07:11:34.2653697Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:494: UserWarning: The environment variable 'USE_MKLDNN' is undefined.
2023-07-07T07:11:34.2654012Z   warnings.warn(
2023-07-07T07:11:34.2654447Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:494: UserWarning: The environment variable 'USE_NNPACK' is undefined.
2023-07-07T07:11:34.2654750Z   warnings.warn(
2023-07-07T07:11:34.2655175Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:494: UserWarning: The environment variable 'USE_QNNPACK' is undefined.
2023-07-07T07:11:34.2655491Z   warnings.warn(
2023-07-07T07:11:34.2655901Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:494: UserWarning: The environment variable 'BUILD_TEST' is undefined.
2023-07-07T07:11:34.2656212Z   warnings.warn(
2023-07-07T07:11:34.2656902Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:499: UserWarning: The environment variable '_GLIBCXX_USE_CXX11_ABI' is being passed through with value '0'.  If you are splitting build and test phases with --no-test, please ensure that this value is also set similarly at test time.
2023-07-07T07:11:34.2657372Z   warnings.warn(
2023-07-07T07:11:34.2657822Z /opt/conda/lib/python3.10/site-packages/conda_build/environ.py:494: UserWarning: The environment variable 'OVERRIDE_TORCH_CUDA_ARCH_LIST' is undefined.
2023-07-07T07:11:34.2658156Z   warnings.warn(