systemd: Re-enable BPF support on powerpc64le

[OPNA2608]

Missing header was due to missing defines. Our Meson cross setup didn't set the correct cpu_family value for little-endian POWER, so upstream's Meson code can't identify the platform correctly and doesn't pass some necessary flags to the compiler.

With #428810 merged, this builds again.

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • powerpc64le-linux (cross)
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

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[flokli]

I don't see a change in the derivation hash (nix-instantiate -A systemd --argstr system powerpc64-unknown-linux-gnuabielfv1, as well as nix-instantiate -A pkgsCross.ppc64-elfv1.systemd --argstr system aarch64-linux - that is, d5b6a55 with the following cherry-picked on top:

• cc-wrapper: Workaround gnuabielfv{1,2} support deficiency on Clang
• ncurses: Add patch to recognise linux-gnuabielfv{1,2}
• kexec-tools: Only force ELFv2 on ppc64 when the platform settings aggree
• this PR (vs without this PR)

How am I holding this wrong?

[OPNA2608]

It's for powerpc64le-linux. So either -A systemd --argstr crossSystem powerpc64le-linux or -A pkgsCross.powernv.systemd.

(This one should work without applying any other commits, unless something seriously broke about ppc64le cross since I opened this)

[flokli]

Yes, you're right, and the build succeeds.