Fix flatcc path for Windows

[SS-JIA]

Summary

This PR is based on #4993 but includes an additional fix to use the correct equivalent of the rm -rf command for Windows.

Test plan

Built ExecuTorch for Windows using the following command:

del -Recurse -Force cmake-out; `
  cmake . `
  -DCMAKE_INSTALL_PREFIX=cmake-out `
  -DPYTHON_EXECUTABLE=C:\\Users\\ssjia\\AppData\\Local\\miniconda3\\python.exe `
  -DCMAKE_PREFIX_PATH=C:\\Users\\ssjia\\AppData\\Local\\miniconda3\\Lib\\site-packages `
  -DCMAKE_BUILD_TYPE=Release `
  -DEXECUTORCH_BUILD_EXTENSION_TENSOR=ON `
  -T ClangCL `
  -Bcmake-out; `
  cmake --build cmake-out -j64 --target install

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/8970

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❌ 1 New Failure

As of commit fce39dc with merge base 6eee931 ():

NEW FAILURE - The following job has failed:

• pull / unittest / linux / linux-job (gh)
  backends/xnnpack/test/ops/test_conv1d.py::TestConv1d::test_qs8_conv1d_batchnorm_seq

This comment was automatically generated by Dr. CI and updates every 15 minutes.

[tarun292]

Remove these?

[SS-JIA]

oh, good catch :p

[tarun292]

rm -rf in a cmakefile makes me a little uneasy, why do we need this?

[SS-JIA]

I don't know; rm -rf was being used before my changes. Here I'm simply switching it to use a cmd.exe equivalent for Windows. I can change it to rm -r if that's more reasonable.

[tarun292]

ah ok looks like it was there before, so hopefully should be fine i guess

[SS-JIA]

• Removed debug logging
• Removed force flags from rm commands

cc: @tarun292

[SS-JIA]

test failure is most probably unrelated.