GCC and CMake do not work properly on macOS

[Bouncner]

GCC 14 works just fine on macOS, but there are issues with CMake that block us from enabling GCC on macOS.

CMake 3.30 will fix this issue (https://gitlab.kitware.com/cmake/cmake/-/merge_requests/9483).

[Bouncner]

There is another issue with GCC and using the pretty outdated libc++ shipped with macOS.

GCC (rightfully) complains about the usage of std::atomic_load in our code. But we cannot used std::atomic<std::shared_ptr>> as the macOS shipped libc++ has not yet a shared_ptr (was it trivially constructable? I don't remember) that is usable with std::atomic.

So it might take a while until we can use GCC on macOS (check for "atomic" and "shared_ptr" and Apple Clang support here: https://en.cppreference.com/w/cpp/compiler_support).