[webkit-dev] GCC 10 upgrade and C++20 availability

Hello WebKittens, Now, based on milestone, we upgraded GCC requirement from 9.3 to 10.2. This further unlocks many C++20 features, like <=> operator and constinit You can see more C++20 features in https://en.cppreference.com/w/cpp/20 Best regards, -Yusuke