Add GCC 16.1

[Bronek]

GCC 16 was released two weeks ago, let's add it to available images

[mathbunnyru]

We'll be moving away from multiple images (and this repo), please see XRPLF/rippled#7083

This also creates too much duplication (yet again)

So, I suggest not to merge this, and not to work on this right now, because threre will be better ways of doing things quite soon

[Bronek]

@mathbunnyru is that new nix image also going to provide gcc for Debian builds, or is GCC 16 going to land only in nix ?

[mathbunnyru]

@mathbunnyru is that new nix image also going to provide gcc for Debian builds, or is GCC 16 going to land only in nix ?

We might not even have separate "debian" build, because the nix provides fully isolated environment. This hasn't been decided yet

But, what's going to happen (in short) is the following:

1. Tools will be provided by nix
2. Compilers and standard library as well
3. We'll pin libc version to the oldest we need to support
4. Only one gcc and only one clang will be supported (usually, quite recent) - there will be no promise of being able to build with old compilers
5. The configuration matrix will be heavily simplified (but keeping all the important stuff, like we'll still have sanitized builds)