more-exhaustive stdenv-exercising expression (non-Hydra)

[ghost]

My experience with #209870 has showed me that there are a lot of important expressions which major stdenv refactors are likely to break, yet which are not exercised by Hydra builds. Current examples:

• pkgsMusl.stdenv
• stdenv --argstr localSystem aarch64-darwin
• exotic architectures like powerpc64, mips64, riscv64
• something that uses gfortran (nothing in the "small" Hydra set uses it)
• pkgsCross.$something.stdenv

I would like to start collecting a list of these expressions somewhere in nixpkgs, as a reminder for future stdenv overhauls. The idea here is that Hydra won't build these, but anybody doing major work on stdenv should at least look at the list and decide for themselves which of the test builds ought to be run. In some cases this will require pinging people who have access to exotic hardware, or using an emulator, so none of these test expressions will be mandatory. But authors should at least consider each expression on the list and make their own judgment call regarding whether or not that test is worth the effort for their PR.

If you have any recommendations for expressions to put on this list, please post them here.

If the list gets too big I will sort it and/or partition it into tiers.

I'd like to store the expression list somewhere in nixpkgs, so reviewers can ask ofborg to build one if they think it is particularly relevant.

[ghost]

Closed by #243321