(doc): set cmake c++ compatible standard when building on MacOS CPU.

[teekenl]

Purpose

When building source on MacOS (CPU), encountered compilation error: 'constexpr' is not a type, that because clang is defaulting to old c++ standard that seem not able to compile specific syntax properly.

Test Plan

Test Result

(Optional) Documentation Update

Add troubleshotting solution on docs/getting_started/installation/cpu/apple.inc.md

---

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

[gemini-code-assist]

Code Review

This pull request adds documentation for a workaround to a build issue on macOS related to the C++ standard. While adding this troubleshooting guide is helpful for users who might encounter this, a more robust solution would be to address the root cause in the build configuration itself. I recommend updating cmake/cpu_extension.cmake to enforce the required C++ standard, for instance by adding set(CMAKE_CXX_STANDARD 17). This would prevent the issue from occurring in the first place and provide a smoother experience for developers building on macOS.

[gemini-code-assist]

On macOS, the system compiler is typically Clang, not GCC. Mentioning "old GCC standard" could be misleading for users on this platform. To improve clarity and accuracy, I recommend referring to the C++ standard more generally.

For example:

    **Solution**: Your compiler might be using an older C++ standard. Edit `cmake/cpu_extension.cmake` and add `set(CMAKE_CXX_STANDARD 17)` before `set(CMAKE_CXX_STANDARD_REQUIRED ON)`.

[teekenl]

good idea! updated now

[hmellor]

LGTM! Thanks for adding this troubleshooting tip!