lib.systems.examples: canonicalize MIPS triples

[alyssais]

Description of changes

In Nixpkgs, we assume that the "config" field is a canonicalized GNU
triple. I noticed that non-canonical values were being used here,
because the pkgsCross.mips64el-linux-gnu triples did not contain the
vendor field, but the pkgsCross.mips64el-linux-gnu.pkgsStatic did.

Here, I've run all the MIPS triples in lib.systems.examples through
config.sub to canonicalize them. I think this will avoid nasty
surprises in future.

Tested by building Nix and the bootstrap files for
pkgsCross.mips64el-linux-gnu.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 22.11 Release Notes (or backporting 22.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

cc @amjoseph-nixpkgs

[symphorien]

In Nixpkgs, we assume that the "config" field is a canonicalized GNU
triple

is this documented somewhere ?

[alyssais]

In Nixpkgs, we assume that the "config" field is a canonicalized GNU
triple

is this documented somewhere ?

No, in fact the documentation claims otherwise. But I don't think we're using LLVM triples in practice. Perhaps @sternenseemann or @Ericson2314 can weigh in here?

[ghost]

I'm re-running the mips64el bootstrap with this change. It'll take a day or so to finish, but I doubt there will be any problems.

[ghost]

But I don't think we're using LLVM triples in practice.

I don't think so either. What we're using are either autoconf tuples or multiarch tuples. They are exactly the same thing except in two cases involving older 32-bit architectures.

In Nixpkgs, we assume that the "config" field is a canonicalized GNU triple

is this documented somewhere ?

Suggested documentation: #180030

[sternenseemann]

But I don't think we're using LLVM triples in practice.

It's a bit more complicated than that. We generally follow autoconf (since Nix is using that), but deviate from it in practical behavior (#165836) as well as nomenclature/semantics. Additionally in practice we assume that the canonicalized nixpkgs config attribute is interpreted in the same way by autoconf as well as LLVM, as it ends up being passed to clang via -target for example.