pkgs/top-level: do not forbid cross-builds from powerpc64le

[ghost]

Description of changes

This commit tells nixpkgs that it's okay to attempt cross-compiles from powerpc64le. These machines are exceptionally fast, they're great for doing large builds.

Things done

• Built on platform(s)
  • powerpc64le-linux
• 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
• Fits CONTRIBUTING.md.

[Mindavi]

Hmm, I thought this list was more meant for hydra to use

[ghost]

Hmm, I thought this list was more meant for hydra to use

Unfortunately this assertion triggers even outside of Hydra:

nixpkgs/pkgs/top-level/release-cross.nix

Line 212 in fdf0c55

assert lib.elem drv.system supportedSystems;

Would you prefer that I change this PR to remove the assertion? It obstructs attempts to run otherwise-valid builds.

$ uname -m
ppc64le

$ nix-build pkgs/top-level/release-cross.nix -A bootstrapTools.mips64el-linux-gnuabi64
error: assertion '((lib).elem (drv).system supportedSystems)' failed

       at /nix/nixpkgs/pkgs/top-level/release-cross.nix:219:7:

          218|     mkBootstrapToolsJob = drv:
          219|       assert lib.elem drv.system supportedSystems;
             |       ^
          220|       hydraJob' (lib.addMetaAttrs { inherit maintainers; } drv);

[vcunat]

The pkgs/top-level/release*.nix files are designed only for Hydra.nixos.org right now, so this would introduce jobs in there which it couldn't run and they would accumulate in queue. Still the list can be overridden on command line and the Hydra's jobset allows configuring that as well, so it certainly could be done without issues (most likely), but it would be a change in the current design.

[ghost]

Thanks for explaining! Makes sense now.