Arm backend: Build c/c++ code with -Wall -Werror

[zingo]

This allows better detection of bad code.

cc @digantdesai @freddan80 @per @oscarandersson8218

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/11815

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✅ You can merge normally! (4 Unrelated Failures)

As of commit 2809e5a with merge base 28905e7 ():

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• trunk / test-apple-model / macos-job (gh) (similar failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• trunk / test-llama-torchao-lowbit / macos-job (gh) (similar failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• trunk / test-models-macos (resnet50, xnnpack-quantization-delegation) / macos-job (gh) (similar failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

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

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

• pull / unittest-buck / 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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