clang now maps to Homebrew clang not Apple clang

[vszakats]

Description

After 0260317.0218.1, clang command maps to /opt/homebrew/bin/clang,
while earlier it mapped to Apple clang at /usr/bin/clang.

Was it intented?

Platforms affected

• Azure DevOps
• GitHub Actions - Standard Runners
• GitHub Actions - Larger Runners

Runner images affected

• Ubuntu 22.04
• Ubuntu 24.04
• Ubuntu Slim
• macOS 14
• macOS 14 Arm64
• macOS 15
• macOS 15 Arm64
• macOS 26
• macOS 26 Arm64
• Windows Server 2022
• Windows Server 2025
• Windows Server 2025 with Visual Studio 2026

Image version and build link

Image: macos-15-arm64
Version: 20260317.0218.1
Included Software: https://github.com/actions/runner-images/blob/macos-15-arm64/20260317.0218/images/macos/macos-15-arm64-Readme.md
Image Release: https://github.com/actions/runner-images/releases/tag/macos-15-arm64%2F20260317.0218

Last known good:
Image: macos-15-arm64
Version: 20260303.0188.2
Included Software: https://github.com/actions/runner-images/blob/macos-15-arm64/20260303.0188/images/macos/macos-15-arm64-Readme.md
Image Release: https://github.com/actions/runner-images/releases/tag/macos-15-arm64%2F20260303.0188

Is it regression?

yes

Expected behavior

clang command maps to Apple clang.

Actual behavior

clang command maps to Homebrew llvm/clang 18

Repro steps

$ which clang

[ldionne]

I can confirm noticing this change as well and tracing it to the new image version released today. See llvm/llvm-project#187541 (comment)

Since there is a large difference between the Clang that ships with Xcode 26.x and Homebrew clang included by default in the image, both are not interchangeable at all and I expect this to break many CI setups.

[zhangskz]

We are hitting this in our CI as well, namely in the form of --implicit-int-float-conversion errors (which should not be errors by default in Clang 15.0.7 that the image claims to ship with) and clang: error: invalid linker name in argument '-fuse-ld=ld64.lld:'