Arm backend: Refactor compiler choices in setup.sh

[perheld]

Introduce helper scripts for toolchains to not clutter up setup.sh too
much with all the combinations of platform, os and compiler options.

Change-Id: I9293c92604f45bb7e4e83c0af5be4adbdce4592e
Signed-off-by: per.held@arm.com

[pytorch-bot]

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❌ 5 New Failures

As of commit d0edb28 with merge base cec1400 ():

NEW FAILURES - The following jobs have failed:

• Build documentation / build (buck2) / Build doc (gh)
• pull / unittest-nxp-neutron / linux-job (gh)
  RuntimeError: Command docker exec -t d7f5af5e5acc4d78e64e515f3fce64fb55809055a61a0c543244814671fbe751 /exec failed with exit code 1
• trunk / test-huggingface-transformers-macos (llama3.2-1b|coreml_fp32_gpu|--quantize) / macos-job (gh)
  The process '/opt/homebrew/bin/git' failed with exit code 128
• trunk / test-llama-runner-mac (fp32, coreml) / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• trunk / test-models-linux-aarch64 (qwen2_5, portable, linux.arm64.2xlarge) / linux-job (gh)
  RuntimeError: Command docker exec -t 561ac23e251bcbca3e66c7f35eac442539e5cfacff2086e07f32bfd79da39baa /exec failed with exit code 1

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