Fix Cadence CPU runner CMake build

[aliafzal]

Summary

• Detect lib vs lib64 install directory in build_cadence_runner.sh
• Add -DPYTHON_EXECUTABLE to prevent GLOB_RECURSE scanning entire filesystem when variable is unset
• Update generic/operators/CMakeLists.txt with actual source filenames

Test plan

• Built cadence_runner successfully on devvm (CentOS/lib64 system)
• Verified cmake configure completes without hanging
• Verified cadence_runner binary is produced at cmake-out/backends/cadence/cadence_runner

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/18021

• 📄 Preview Python docs built from this PR

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❌ 4 New Failures, 24 Pending

As of commit b3190ac with merge base 7b5c60d ():

NEW FAILURES - The following jobs have failed:

• pull / test-llama-runner-qnn-linux (fp32, qnn_8a8w, qnn) / linux-job (gh)
  RuntimeError: Command docker exec -t d098a724e53d11cfa52775d6da7a7311a0e0b26b0371a044f5e91217150cc84e /exec failed with exit code 92
• Test Metal Backend / export-model-metal-artifact (mistralai, Voxtral-Mini-3B-2507, quantized-int4-metal) / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• Test Metal Backend / export-model-metal-artifact (mistralai, Voxtral-Mini-4B-Realtime-2602, quantized-int4-metal) / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• Test Metal Backend / export-model-metal-artifact (openai, whisper-large-v3-turbo, non-quantized) / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

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[meta-codesync]

@aliafzal has imported this pull request. If you are a Meta employee, you can view this in D95846702.

[meta-codesync]

@aliafzal has exported this pull request. If you are a Meta employee, you can view the originating Diff in D95846702.