[build] `ystdlib` dependency fails to build on older macOS

[sitaowang1998]

Bug

#1038 introduces installing ystdlib as a CMake package. However, on macOS, all dependencies are built with AppleClang instead of clang++ from llvm@16 installed through homebrew. On older macOS, i.e. macOS-13 and macOS-14, the old versions of AppleClang do not support C++ 20, which is required by ystdlib. Thus, ystdlib cannot be built on these platforms. #1038 temporarily disables GitHub workflows for these two platforms.

Solutions explored

We have tried to set up environment variables LLVM_PREFIX, CC, CXX, AR, RANLIB through GITHUB_ENV to instruct CMake to use clang++ to build all dependencies. However, the environment variables confuses clang-tidy to use llvm@16 system libraries, while clp and all dependencies are built using macOS sdk system libraries for compatibility with homebrew installed libraries.

CLP version

6815890

Environment

macOS-13 and macOS-14

Reproduction steps

GitHub workflows fail