Fix build on Windows, re-enable Windows build CI job

[GregoryComer]

CMake doesn't seem to like empty exclude patterns.

[GregoryComer]

Stack from ghstack (oldest at bottom):

• -> Fix build on Windows, re-enable Windows build CI job #13672

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/13672

• 📄 Preview Python docs built from this PR

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❌ 2 New Failures, 2 Unrelated Failures

As of commit 3a32779 with merge base 7dab7c1 ():

NEW FAILURES - The following jobs have failed:

• Build documentation / build (buck2) / Build doc (gh)
  At least one of the pre-conditions you specified did not hold
• Build Presets / windows (pybind) / build (gh)

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

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

• pull / unittest / macos / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• pull / unittest-editable / macos / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

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[GregoryComer]

@swolchok It looks like CMake complains when there's an exclude with an empty pattern (see https://github.com/pytorch/executorch/actions/runs/17222786697/job/48861521892, line 818). This is a bit of a pain as there doesn't seem to be an elegant solution to this. Do you have any preferences on this approach?

I suppose we could default the exclude pattern to some string that matches nothing, though that seems a little hacky. It looks like we could also maybe build a list of install args, including the "magic" keywords, though I haven't tried it.