build: add clang ci

[egolearner]

Greptile Summary

This PR adds a new Clang CI job for linux-x64 by introducing an optional compiler input to the reusable build workflow and a corresponding new pipeline job. The changes are well-scoped and the previously flagged missing OS guard on the Install Clang step has been correctly addressed.

Key changes:

• 01-ci-pipeline.yml: Adds build-and-test-linux-x64-clang job that calls the reusable workflow with compiler: clang on ubuntu-24.04.
• 03-macos-linux-build.yml: Adds optional compiler input (defaults to ''); installs clang and libomp-dev via apt on Linux when compiler == 'clang'; exports CC=clang / CXX=clang++ for the build steps.
• The Install Clang step is correctly guarded with inputs.compiler == 'clang' && runner.os == 'Linux'.
• Minor inconsistency: the env-var block that sets CC/CXX does not carry the same runner.os == 'Linux' guard, which could produce unexpected behaviour if the workflow is extended to macOS clang builds in the future.

Confidence Score: 4/5

• Safe to merge; one minor style inconsistency around the OS guard on the compiler env-var block.
• The core logic is correct and the previously raised critical issue (missing OS guard on the install step) has been fixed. The only remaining observation is a minor inconsistency where CC/CXX are set without a runner.os == 'Linux' guard, which does not affect the current job configuration but could silently misbehave if a future macOS clang job is added.
• 03-macos-linux-build.yml — specifically the compiler env-var block at lines 74–77.

Important Files Changed

Filename	Overview
.github/workflows/01-ci-pipeline.yml	Adds a new build-and-test-linux-x64-clang job that calls the reusable build workflow with compiler: clang on ubuntu-24.04; straightforward and correct.
.github/workflows/03-macos-linux-build.yml	Adds optional compiler input, installs Clang + libomp-dev on Linux when requested, and exports CC/CXX. The install step is correctly OS-guarded, but the env-var block that sets CC/CXX lacks the same guard, creating a minor inconsistency if the workflow is reused on macOS with compiler: clang.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A([Push / PR / workflow_dispatch]) --> B[lint job]

    B --> C[build-and-test-macos-arm64\nmacos-15]
    B --> D[build-and-test-linux-arm64\nubuntu-24.04-arm]
    B --> E[build-and-test-linux-x64\nubuntu-24.04 / gcc]
    B --> F[build-and-test-linux-x64-clang\nubuntu-24.04 / clang ✨NEW]
    B --> G[build-android]

    subgraph reusable ["03-macos-linux-build.yml  (reusable)"]
        H[Checkout + Setup Python]
        H --> I{compiler == clang\n&& runner.os == Linux?}
        I -- yes --> J[apt install clang libomp-dev]
        I -- no --> K[Skip install]
        J --> L[Set up env vars\nCC=clang CXX=clang++]
        K --> L
        L --> M[pip install dependencies]
        M --> N[Build from source\npython -m pip install]
        N --> O[Run C++ Tests]
        O --> P[Run Python Tests]
        P --> Q[Run C++ Examples]
    end

    F --> reusable
    E --> reusable
    C --> reusable
    D --> reusable

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_{Reviews (3): Last reviewed commit: "address comments" | Re-trigger Greptile}

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