When new GCC versions change the default C or C++ standard, we often end up having various packages break because they're old and sometimes the patches needed to fix them are pretty huge, so we do append-flags -std=gnu89 or whatever and move on when appropriate. However, when something starts using *new* features and e.g. doesn't use pkg-config correctly to force that in reverse dependencies, we need to do something like append-flags -std=c++17 in ebuilds until the compilers catch up. Once the compilers do catch up, we don't want to keep setting it, as it regresses from whatever the default is (goes backwards). We should have: 1. default-c-std 2. default-cxx-std or similar
