- [regression testing]: the macOS Command Line Tools for Xcode 26.3 clang 'integrated assembler' warns about overriding deployment version from '16.0' to '26.0' invoked from these compilers
- special case handling for macOS Homebrew LLVM C/C++ compiler versions 16-20: add flag '-mmacosx-version-min=<macOS major version>.0' to 'AM_CXXFLAGS'
- [regression testing]: avoid warnings from the macOS Command Line Tools for Xcode 26.3 clang when linking with libraries built for macOS version 26.0
- drop special case handling for Homebrew C/C++ compiler version 5
