gnustep.(base|gui): fix icu 68 compatibility

[ajs124]

Motivation for this change

Doesn't compile on master after #107774 / unicode-org/icu@c3fe7e09d844

We could also stick with icu 67.x instead.

cc @marsam (please tell me if I should stop pinging you on these)

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) (sogo)
• 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.

[rmcgibbo]

Here's the result from @r-rmcgibbo, which for some reason crashed while trying to upload the comment

---

Result of nixpkgs-review pr 114667 at 71c43913 run on x86_64-linux 1

9 packages failed to build:

• bookworm
• gnustep.back
• gnustep.gorm
• gnustep.gui
• gnustep.gworkspace
• gnustep.projectcenter
• gnustep.system_preferences
• openvpn-auth-ldap
• pikopixel

4 packages built:

• gnustep.base
• sogo
• sope
• unar

1 suggestion:

• warning: missing-patch-comment

  Please add a comment on the line above, explaining the purpose of this patch.
  Near pkgs/desktops/gnustep/base/default.nix:36:15:

     |
  36 |   patches = [ ./fixup-paths.patch ];
     |               ^
  

[ajs124]

oof, looks like other gnustep components also relied on those #defines

[marsam]

please continue pinging me on all the icu 68 related issues :)

[marsam]

Thank you!