Fix setup.py to skip CPU kernels on Windows

[Xia-Weiwen]

Fixes #3175

CPU kernel files in the torchao/csrc/cpu/aten_kernels/ directory are not skipped correctly on Windows because the path string matching fails (\ vs /). This PR fixes this issue.

Test plan
We need a CI flow that tests building Torchao on Windows

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/ao/3187

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✅ You can merge normally! (2 Unrelated Failures)

As of commit a3d79ab with merge base ca99c1c ():

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• Run Regression Tests (aarch64) / test-cpu-ops (linux.arm64.2xlarge) (gh) (trunk failure)
  ##[error]The operation was canceled.
• Run Regression Tests (aarch64) / test-cpu-ops (macos-14) (gh) (trunk failure)
  /Users/runner/miniconda3/envs/venv/lib/python3.10/site-packages/executorch/share/cmake/../../include/executorch/runtime/core/memory_allocator.h:143:21: error: no matching function for call to 'mul_overflows'

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[Xia-Weiwen]

CI is broken. Failures are not related to this PR.

[Xia-Weiwen]

@mingfeima Please review. Thanks.

[Xia-Weiwen]

Hi @vkuzo @jerryzh168 @metascroy @mingfeima @Valentine233 Please review this PR. Thanks.

[Xia-Weiwen]

Hi @vkuzo @jerryzh168 @metascroy Can you please review this PR? Thanks.

[Xia-Weiwen]

Hi @vkuzo @jerryzh168 @metascroy Can you please review this PR? Thanks.

[vkuzo]

could you add a test plan detailing how this was tested for correctness? Thank you!

[Xia-Weiwen]

could you add a test plan detailing how this was tested for correctness? Thank you!

Hi @vkuzo If there is a CI workflow that builds Torchao on Windows, this will be tested. Do you have a plan to enable that in CI? Thanks.

[Xia-Weiwen]

Hi @vkuzo I have submitted an issue here #3237 Can we add such a workflow in CI to test it? Thanks.