Enable audio build on Windows with CUDA

[mszhanyi]

With this PR, audio could be build on Windows with CUDA now.
It's from #1777
I've verified it locally.

[mszhanyi]

@mthrok
Did you miss removing something related in this commit.
0f82217#diff-1e7de1ae2d059d21e1dd75d5812d5a34b0222cef273b7c3a2af62eb747f9d20a

without this, there's one error locally.

cc @malfet

[malfet]

LGTM if CI is green

[malfet]

But that wouldn't work when TorchAudio is compiled with CUDA-10.2, would it?

[mszhanyi]

It would.
https://app.circleci.com/pipelines/github/pytorch/audio/7396/workflows/058b3c2c-8421-40c2-915c-a8441deac091/jobs/339245.
It's a Visual Studio Issue. I verified that another workaround is to downgrade the Visual Studio to 16.8.5 which PyTorch Builder is using.
But I think user experience might better that the user doesn't need to select the compiler with the specific version.

[mszhanyi]

The root cause is a regression in VS. microsoft/STL#2020

[mthrok]

@mthrok
Did you miss removing something related in this commit.
0f82217#diff-1e7de1ae2d059d21e1dd75d5812d5a34b0222cef273b7c3a2af62eb747f9d20a

without this, there's one error locally.

cc @malfet

The deletion itself is as-intended. The option was removed because libtorchaudio should be built all the time. libtorchaudio is where all the C++ implementation that do not require libpython dependency is placed.

What I might have missed is to check if the extension .dll is/should be recognized by setuptools.

The logic there is that;

1. python setup.py build_ext invokes the compilation of extension module, expecting torchaudio._torchaudio and torchaudio.lib.libtorchaudio.
2. cmake builds libtorchaudio and _torchaudio.
   For Linux and macOS they are libtorchaudio.so and _torchaudio.so. For Windows _torchaudio has to have pyd extension but I am not sure about libtorchaudio as it is C++ library without any Python component.
3. python setup.py install picks up the compiled modules from build directory and place it in the installation location.
   Your error indicates that setuptools expect the libtorchaudio to have extension .pyd but, currently CMake produces libtorchaudio.dll thus setuptools cannot find libtorchaudio.

I am not sure what's the right fix for Windows, but one way it might work is to set the extension of libtorchaudio to pyd as well. You can try adding this for libtorchaudio here, then change this line from dll to pyd.

[mszhanyi]

I am not sure what's the right fix for Windows, but one way it might work is to set the extension of libtorchaudio to pyd as well. You can try adding this for libtorchaudio here, then change this line from dll to pyd.

Thanks @mthrok . It works now. I've submitted another PR #1788 for these change.
Once #1788 is merged, It can be merged.