🐛 Describe the bug

We have code in aten/src/ATen/cpu/vec/ gated on CPU_CAPABILITY_NEON, such as

. Nothing except torchinductor appears to define this macro, and it's certainly not defined during python setup.py install on my Mac (as determined by putting an #error in one of the blocks gated on #if defined(CPU_CAPABILITY_NEON).

Versions

Collecting environment information...
PyTorch version: N/A
Is debug build: N/A
CUDA used to build PyTorch: N/A
ROCM used to build PyTorch: N/A

OS: macOS 14.7 (arm64)
GCC version: Could not collect
Clang version: 16.0.0 (clang-1600.0.26.3)
CMake version: version 3.30.4
Libc version: N/A

Python version: 3.12.4 | packaged by Anaconda, Inc. | (main, Jun 18 2024, 10:07:17) [Clang 14.0.6 ] (64-bit runtime)
Python platform: macOS-14.7-arm64-arm-64bit
Is CUDA available: N/A
CUDA runtime version: Could not collect
CUDA_MODULE_LOADING set to: N/A
GPU models and configuration: Could not collect
Nvidia driver version: Could not collect
cuDNN version: Could not collect
HIP runtime version: N/A
MIOpen runtime version: N/A
Is XNNPACK available: N/A

CPU:
Apple M1 Pro

Versions of relevant libraries:
[pip3] executorch==0.4.0a0+9d9cda0
[pip3] mypy==1.10.0
[pip3] mypy-extensions==1.0.0
[pip3] numpy==1.26.4
[pip3] optree==0.12.1
[pip3] torch==2.6.0a0+gitccca3de
[pip3] torchao==0.5.0+git0916b5b
[pip3] torchaudio==2.4.0.dev20240716
[pip3] torchsr==1.0.4
[pip3] torchvision==0.20.0.dev20240716
[conda] executorch 0.4.0a0+9d9cda0 pypi_0 pypi
[conda] numpy 2.0.1 pypi_0 pypi
[conda] numpy-base 1.26.4 py312he047099_0
[conda] optree 0.12.1 pypi_0 pypi
[conda] torch 2.6.0a0+gitccca3de pypi_0 pypi
[conda] torchao 0.1 pypi_0 pypi
[conda] torchaudio 2.4.0.dev20240716 pypi_0 pypi
[conda] torchsr 1.0.4 pypi_0 pypi
[conda] torchvision 0.20.0.dev20240716 pypi_0 pypi

cc @malfet @seemethere @snadampal @milpuz01 @ezyang @chauhang @penguinwu @voznesenskym @EikanWang @jgong5 @Guobing-Chen @XiaobingSuper @zhuhaozhe @blzheng @wenzhe-nrv @jiayisunx @ipiszy @yf225 @chenyang78 @kadeng @muchulee8 @ColinPeppler @amjames @desertfire