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 [email protected]
  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.

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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.

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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

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.01%. Comparing base (fb39755) to head (47bb847).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7510   +/-   ##
=======================================
  Coverage   69.01%   69.01%           
=======================================
  Files        1482     1482           
  Lines      273999   273999           
  Branches    28258    28258           
=======================================
+ Hits       189093   189107   +14     
+ Misses      77520    77508   -12     
+ Partials     7386     7384    -2     

Flag	Coverage Δ
Debug	69.01% <ø> (+<0.01%)	⬆️
production	63.31% <ø> (+<0.01%)	⬆️
test	89.46% <ø> (ø)

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