macOS x64 CI: fix dependency install and OpenMP runtime copy (use Homebrew libomp, adjust Helix payload)

[asp2286]

PR: macOS x64 CI: fix dependency install and OpenMP runtime copy

Summary

This PR fixes MachineLearning-CI failures on macOS x64 where jobs stop at Install MacOS build dependencies with:

Bash exited with code '1' 

The breakage comes from two areas:

1. Dependency install: The pipeline relied on a custom libomp.rb path that no longer works on hosted macOS images.
2. Helix payload: The script attempted to copy both libomp.dylib and libiomp5.dylib, but libiomp5.dylib is not available when installing libomp from Homebrew core.

Fixes #7509

---

Changes

build/ci/job-template.yml

• Replace custom brew install …/build/libomp.rb with standard Homebrew:

  brew update brew install -f --overwrite python@3.13 brew install libomp brew link libomp --force

• Note added: Homebrew ≥4.6 rejects installing formulae from raw paths.

eng/helix.proj

• macOS x64 only:
  • Set DYLD_LIBRARY_PATH so Helix can find libomp.dylib.
  • Copy only /usr/local/opt/libomp/lib/libomp.dylib into the publish folder.
  • Remove copying of libiomp5.dylib (not present with libomp from Homebrew).
  • Add install-name fix so binaries reference @loader_path/libomp.dylib.

---

Why

• Hosted macOS runners changed: raw formula paths are blocked, and only libomp is available via core.
• Ensures reliable dependency install and payload runtime linking.
• Other platforms (Linux, Windows, macOS arm64) are unaffected.

---

Testing

• Reproduced failure on osx.13.amd64.open queue.
• With these changes:
  • Dependency install step completes successfully.
  • libomp.dylib is present in publish folder.
  • Helix payload runs with DYLD_LIBRARY_PATH set correctly.
• Validated in a test run: both macOS x64 Debug/Release proceed past dependency install and build succeeds.

---

Risk / Impact

• Low: scoped only to macOS x64 build dependencies and Helix payload.
• No product code changes, only CI infra adjustments.

---

Additional Notes

• Linux and Windows jobs were already green.
• If maintainers prefer llvm over libomp as the OpenMP provider, happy to adjust.

---

PR Checklist

• CLA signed
• Tests: N/A (CI infra only)
• Docs: N/A (no public-facing change)
• Breaking change: No
• Linked issue: MacOS_x64 Debug/Release build jobs fail in MachineLearning-CI: “Bash exited with code '1' – Install MacOS build dependencies” #7509

[azure-pipelines]

Commenter does not have sufficient privileges for PR 7510 in repo dotnet/machinelearning

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.00%. Comparing base (fb39755) to head (1390b39).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@ ## main #7510 +/- ## ========================================== - Coverage 69.01% 69.00% -0.01%  ========================================== Files 1482 1482 Lines 273999 273999 Branches 28258 28258 ========================================== - Hits 189093 189075 -18  - Misses 77520 77536 +16  - Partials 7386 7388 +2 

Flag	Coverage Δ
Debug	69.00% <ø> (-0.01%)	⬇️
production	63.29% <ø> (-0.01%)	⬇️
test	89.46% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.
see 5 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[azure-pipelines]

Commenter does not have sufficient privileges for PR 7510 in repo dotnet/machinelearning

[asp2286]

@artl93 @ericstj Could you please review this PR? Thank you!

[skyRoma]

I really need these changes, thanks!

[ericstj]

I tried to simplify a bit where x64 and M1 were the same. Let's see if this will also resolve the M1 failure.

[asp2286]

/ba-g Mac-OS unrelated failures