Undocumented new variable CMAKE_C_COMPILER_FRONTEND_VARIANT breaking existing toolchain files.
It seems a new (internal?) variable
CMAKE_C_COMPILER_FRONTEND_VARIANT was introduced in CMake 3.15.0 and broke detection of C++ feature for some toolchain files, including the emscripten one.
This change was not in the release notes, nor is it documented, which led to the following issue https://github.com/emscripten-core/emscripten/issues/9100 and resolution https://github.com/emscripten-core/emscripten/pull/9102.
I understand that the issue might be because of the toolchain file itself.
However, if that really is an internal variable could you please explain how we should (know how to) write our toolchain files to be compatible with
CXX_STANDARD properties without it breaking in the future ?
Otherwise documentation / mention in release notes would be welcomed.