Cortex_m backend: Simplify CMSIS-NN build

[AdrianLundell]

• Use FetchContent_MakeAvailable to define cmsis-nn target
• Remove custom MVE definition. Instead use the one defined in CMSIS-NN

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/14463

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 4 New Failures, 1 Unrelated Failure

As of commit c3a5be1 with merge base 5ae40f1 ():

NEW FAILURES - The following jobs have failed:

• Lint / android-java-format / linux-job (gh)
  RuntimeError: Command docker exec -t d3a85213999797164ea0ea428a52bee31dfd556777171fb3858417f556677970 /exec failed with exit code 1
• Test CUDA Builds / test-executorch-cuda-build-12.9 / linux-job (gh)
  RuntimeError: Command docker exec -t 4bd84d60f94e254a2b31006bb38f5e2445cc111859790915c1de8cd581c62dbe /exec failed with exit code 1
• trunk / test-arm-ootb-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 86e4ab869b07fb65e530b9957e27407ea407ac990c755018c9351a2d5937599d /exec failed with exit code 1
• trunk / unittest-release / windows / windows-job (gh)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_ic4_model

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

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

• Test CUDA Builds / check-all-cuda-builds (gh) (trunk failure)

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

[AdrianLundell]

Fails does not look related

[zingo]

Arm fail is also unrelated
trunk / test-arm-ootb-linux / linux-job
Work is ongoing to fix it in another PR

[digantdesai]

+1