GCC 11 Upgrade

[poodlewars]

Our build uses GCC 10. I think our code is mostly compatible with GCC 11 (I spent a week working with GCC 11 by mistake, without running in to any issues).

We're using quite a new MSVC, and writing code compatible with that and the old GCC 10 is quite annoying. It cost me a lot of back and forth between the two platforms this week.

We'd need to:

• Upgrade the compiler in the builds (including Conda)
• Update any dev setup notes that refer to a GCC version
• Upgrade the compiler in the internal Man Group dev container

[poodlewars]

I would also be fine with hopping straight to GCC 12, but if it's hard work to support it, the upgrade to GCC 11 in the meantime seems worthwhile.