Tweak `USE_CUDA` detection (#3005)

Summary:
We don't need the presence of physical HW to compile with CUDA.

Likely one of the causes of  https://github.com/pytorch/audio/issues/2979 (i.e. in CircleCI builds USE_CUDA were defined by CI environment, so nobody ever checked the default, but this is not the case in Nova builds)

Pull Request resolved: https://github.com/pytorch/audio/pull/3005

Test Plan:
Check that `compute.cu` is mentioned in builds, for example see https://github.com/pytorch/audio/actions/runs/3990295262/jobs/6843771056#step:9:829
```
[193/202] /usr/local/cuda-11.6/bin/nvcc -forward-unknown-to-host-compiler -DINCLUDE_KALDI -DUSE_C10D_GLOO -DUSE_C10D_NCCL -DUSE_CUDA -DUSE_DISTRIBUTED -DUSE_RPC -DUSE_TENSORPIPE -Dlibtorchaudio_EXPORTS -I/__w/audio/audio/pytorch/audio -I/__w/audio/audio/pytorch/audio/third_party/kaldi/src -I/__w/audio/audio/pytorch/audio/third_party/kaldi/submodule/src -isystem=/__w/_temp/conda_environment_3990295262/lib/python3.7/site-packages/torch/include -isystem=/__w/_temp/conda_environment_3990295262/lib/python3.7/site-packages/torch/include/torch/csrc/api/include -isystem=/usr/local/cuda-11.6/include -DONNX_NAMESPACE=onnx_c2 -gencode arch=compute_35,code=sm_35 -gencode arch=compute_50,code=sm_50 -gencode arch=compute_60,code=sm_60 -gencode arch=compute_70,code=sm_70 -gencode arch=compute_75,code=sm_75 -gencode arch=compute_80,code=sm_80 -gencode arch=compute_86,code=sm_86 -gencode arch=compute_50,code=compute_50 -Xcudafe --diag_suppress=cc_clobber_ignored,--diag_suppress=integer_sign_change,--diag_suppress=useless_using_declaration,--diag_suppress=set_but_not_used,--diag_suppress=field_without_dll_interface,--diag_suppress=base_class_has_different_dll_interface,--diag_suppress=dll_interface_conflict_none_assumed,--diag_suppress=dll_interface_conflict_dllexport_assumed,--diag_suppress=implicit_return_from_non_void_function,--diag_suppress=unsigned_compare_with_zero,--diag_suppress=declared_but_not_referenced,--diag_suppress=bad_friend_decl --expt-relaxed-constexpr --expt-extended-lambda -O3 -DNDEBUG -Xcompiler=-fPIC -D_GLIBCXX_USE_CXX11_ABI=0 -std=c++17 -MD -MT torchaudio/csrc/CMakeFiles/libtorchaudio.dir/rnnt/gpu/compute.cu.o -MF torchaudio/csrc/CMakeFiles/libtorchaudio.dir/rnnt/gpu/compute.cu.o.d -x cu -c /__w/audio/audio/pytorch/audio/torchaudio/csrc/rnnt/gpu/compute.cu -o torchaudio/csrc/CMakeFiles/libtorchaudio.dir/rnnt/gpu/compute.cu.o
```

Reviewed By: mthrok

Differential Revision: D42687455

Pulled By: malfet

fbshipit-source-id: c37ad58cc62439d1268865e9bf0bcb97079a529f

tools/setup_helpers/extension.py

@@ -39,7 +39,7 @@ _BUILD_RNNT = _get_build("BUILD_RNNT", True)
 _BUILD_CTC_DECODER = _get_build("BUILD_CTC_DECODER", True)
 _USE_FFMPEG = _get_build("USE_FFMPEG", False)
 _USE_ROCM = _get_build("USE_ROCM", torch.cuda.is_available() and torch.version.hip is not None)
-_USE_CUDA = _get_build("USE_CUDA", torch.cuda.is_available() and torch.version.hip is None)
+_USE_CUDA = _get_build("USE_CUDA", torch.backends.cuda.is_built() and torch.version.hip is None)
 _USE_OPENMP = _get_build("USE_OPENMP", True) and "ATen parallel backend: OpenMP" in torch.__config__.parallel_info()
 _TORCH_CUDA_ARCH_LIST = os.environ.get("TORCH_CUDA_ARCH_LIST", None)