fix(ci): use subprocess for Triton compile helpers

[tianleiwu]

Summary

This PR replaces shell-based command execution in the Triton compile helper with subprocess.run(), and adds regression tests to lock in that behavior.

Key Changes

• Switched tools/ci_build/compile_triton.py to use subprocess.run() for objcopy and ar execution instead of os.system().
• Added tools/ci_build/test_compile_triton.py to verify the helper functions invoke subprocess-based command execution and preserve the expected working directory and error handling.
• Hardened directory handling in the Triton compile path so the output directory is created safely with os.makedirs(..., exist_ok=True).

Why

The previous shell-based implementation was fragile and harder to test. Using subprocess.run() makes the command execution path explicit, easier to validate, and safer for CI and cross-platform invocation.

Testing

• source .venv/bin/activate && python -m unittest tools.ci_build.test_compile_triton
• source .venv/bin/activate && lintrunner -a

[Copilot]

Pull request overview

This PR updates the Triton AoT compile helper to execute external tooling (objcopy, ar) via subprocess.run() instead of shelling out with os.system(), and adds unit tests intended to regression-test that behavior in CI.

Changes:

• Replaced shell-based objcopy/ar invocations with subprocess.run(..., cwd=..., check=True) in compile_triton.py.
• Added a new unittest module to validate subprocess.run usage (and that os.system is not used).
• Hardened output directory handling for --obj_file paths with no directory component.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 6 comments.

File	Description
tools/ci_build/compile_triton.py	Switches external command execution to subprocess.run() and tweaks output directory creation.
tools/ci_build/test_compile_triton.py	Adds regression tests to validate subprocess-based command execution behavior.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.