GitLab

Summary:
As it is a C++17 feature, and PyTorch and its extensions must still be C++14 compatible, as also specified in the top level CMakeLists.txt:
https://github.com/pytorch/audio/blob/8a0d7b36f7821fe55175f0d4e3ca6299b3817a6c/CMakeLists.txt#L30

Otherwise, it pollutes build logs with noisy
```
/Users/runner/work/test-infra/test-infra/pytorch/audio/torchaudio/csrc/sox/pybind/io.cpp:12:21: warning: nested namespace definition is a C++17 extension; define each namespace separately [-Wc++17-extensions]
namespace torchaudio::sox_io {
                    ^~~~~~~~
                     { namespace sox_io
```

Pull Request resolved: https://github.com/pytorch/audio/pull/2663

Reviewed By: atalman, nateanl

Differential Revision: D39362842

Pulled By: malfet

fbshipit-source-id: f9659d4420f1cc0194990d531455cf59b66c26b9