libgphoto2: fix darwin build

[fullmetalsheep]

Hi,

Originally caught this while building darktable on aarch64-darwin (which has a dependency on libgphoto2)
libgphoto2 fails to build on Darwin with linker errors due to missing _libintl_dgettext symbols. Logs below:

error: Cannot build '/nix/store/w65rxjfygfgqrp3svnnkbhg61k4hyjjy-libgphoto2-2.5.34.drv'.
       Reason: builder failed with exit code 2.
       Output paths:
         /nix/store/8bxlsx24xb0ycc77h3i6hdc5zbwx12hk-libgphoto2-2.5.34
       Last 25 log lines:
       >   CC       ax203/la-library.lo
       >   CC       ax203/la-ax203.lo
       >   CC       ax203/la-ax203_decode_yuv.lo
       >   CC       ax203/la-ax203_decode_yuv_delta.lo
       >   CC       ax203/la-ax203_compress_jpeg.lo
       >   CC       ax203/la-jpeg_memsrcdest.lo
       >   CC       ax203/la-tinyjpeg.lo
       >   CC       ax203/la-jidctflt.lo
       >   CCLD     ax203.la
       > Undefined symbols for architecture arm64:
       >   "_libintl_dgettext", referenced from:
       >       _camera_summary in la-library.o
       >       _camera_manual in la-library.o
       >       _camera_about in la-library.o
       >       _camera_get_config in la-library.o
       >       _camera_set_config in la-library.o
       > ld: symbol(s) not found for architecture arm64
       > clang: error: linker command failed with exit code 1 (use -v to see invocation)
       > make[3]: *** [Makefile:2214: ax203.la] Error 1
       > make[3]: Leaving directory '/nix/var/nix/builds/nix-38571-1052516044/source/camlibs'
       > make[2]: *** [Makefile:4944: all-recursive] Error 1
       > make[2]: Leaving directory '/nix/var/nix/builds/nix-38571-1052516044/source/camlibs'
       > make[1]: *** [Makefile:778: all-recursive] Error 1
       > make[1]: Leaving directory '/nix/var/nix/builds/nix-38571-1052516044/source'
       > make: *** [Makefile:602: all] Error 2
       For full logs, run:
         nix-store -l /nix/store/w65rxjfygfgqrp3svnnkbhg61k4hyjjy-libgphoto2-2.5.34.drv

Fixed by adding gettext to buildInputs when building for Darwin hosts. It should not affect any other platforms.
Tested manually by building both libgphoto2 and the downstream package darktable. They build and function as expected.

Hope this helps,
Thanks!

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • 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.
• Follows the automation/AI policy.

[fullmetalsheep]

I am also happy to add myself to the maintainers list, if that's welcome.

[BatteredBunny]

Suggested change

	gettext # prevents darwin builds from breaking
	gettext

In my opinion this comment is not needed

[fullmetalsheep]

Fair, removed. Thanks!