CMake cannot fine Python.h when building from source

🐛 Describe the bug

I'm attempting to build torchaudio from source, in order to package it for the Homebrew project. (PyTorch is already packaged for Homebrew, so that makes it a lot easier!) However, I'm running into a problem where CMake is unable to find the Python.h header file. It appears that perhaps the CMakeLists.txt file is not searching for it correctly?

Here is a Gist with my work-in-progress Homebrew formula, and the error message that I'm seeing. One of the other Homebrew maintainers (who knows CMake better than I do) noted that it should work if you search for the header file using find_package(Python3 ..., which the top-level CMakeLists.txt file is doing, but only for WIN32, which seems strange. I'm trying to build on a Mac, and getting an error.

Is there someone who can help me figure out how to make this build on Mac?

Versions

0.13.1

Start with the top-level CMakeLists.txt and cmake/TorchAudioHelper.cmake, especially the Python3 package lookup currently limited to WIN32. Reproduce the source build on macOS using the linked Homebrew formula and error details. Done means CMake locates Python.h and the torchaudio build proceeds on that platform.