Fix NixOS cross-compilation SD Image

[flokli]

Fixes #106759.

Motivation for this change

Build NixOS aarch64 sd image by just instantiating the profile, without any required manual hacks in the config.

Apparently, there was very few left to fix #106759 (for aarch64 at least).

polkit can be built without gobject introspection.

With this, I can just

nix-build -E 'let pkgs = (import ./.) {}; in (pkgs.pkgsCross.aarch64-multiplatform.nixos ./nixos/modules/installer/cd-dvd/sd-image-aarch64.nix).sdImage'

… computer go brrr…

And tada, you get a aarch64 image :-)

No more need to manually disable polkit and udisks.

fsck.fat 4.1 (2017-01-24)
Checking we can access the last sector of the filesystem
Boot sector contents:
System ID "mkfs.fat"
Media byte 0xf8 (hard disk)
       512 bytes per logical sector
      2048 bytes per cluster
         4 reserved sectors
First FAT starts at byte 2048 (sector 4)
         2 FATs, 16 bit entries
     30720 bytes per FAT (= 60 sectors)
Root directory starts at byte 63488 (sector 124)
       512 root directory entries
Data area starts at byte 79872 (sector 156)
     15321 data clusters (31377408 bytes)
32 sectors/track, 64 heads
         0 hidden sectors
     61440 sectors total
Checking for unused clusters.
firmware_part.img: 23 files, 11322/15321 clusters
61440+0 records in
61440+0 records out
31457280 bytes (31 MB, 30 MiB) copied, 0.100648 s, 313 MB/s
/nix/store/qg78laagrq3kp5fp0c9107ckapz0fxkw-nixos-sd-image-21.03pre-git-aarch64-linux.img-aarch64-unknown-linux-gnu/sd-image/nixos-sd-image-21.03pre-git-aarch64-linux.img : 25.91%   (4141109248 => 1073112729 bytes, /nix/store/qg78laagrq3kp5fp0c9107ckapz0fxkw-nixos-sd-image-21.03pre-git-aarch64-linux.img-aarch64-unknown-linux-gnu/sd-image/nixos-sd-image-21.03pre-git-aarch64-linux.img.zst)
/nix/store/qg78laagrq3kp5fp0c9107ckapz0fxkw-nixos-sd-image-21.03pre-git-aarch64-linux.img-aarch64-unknown-linux-gnu

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[Atemu]

Didn't test on armv7l but this is a trivial change and should remove the gobject-introspection dependency from the base image.

Probably doesn't even need to go to staging-next, this causes 0 rebuilds on non-cross platforms.

[flokli]

I assumed staging-next to get merged soon anyways, and only did test on that branch.

IIRC, there was more in there necessary to build the full base image.

[FRidh]

I assumed staging-next to get merged soon anyways, and only did test on that branch.

Hopefully in a day or two. Waiting for some aarch64 results.