How did you update to 6.3? I'm on a custom Kubuntu derivative and I can't find a working repository. Not looking forward to compiling GCC first
It's not actually GCC that's the problem, it's the libstdc++ headers, so if you build a new GCC you need to make it build against an updated libstdc++ or it won't solve anything. It's pretty easy to build GCC and make it install to an alternate path. Just add something like this to whatever other configure options you need: