fluent-bit: link against Nix dependencies, fix Darwin builds, and add NixOS module

[commiterate]

Link against Nix dependencies, fix Darwin builds, and add NixOS module (upstreams commiterate/nix-fluent-bit).

fluent-bit vends its dependencies by keeping a copy of their sources under lib/ in their source tree and building them from source. All of the dependencies their CMake setup can source from the system are already Nix packages (e.g. libbacktrace, luajit).

Darwin builds have also been silently broken for awhile now.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• 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
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[arianvp]

I'm gonna give this a test run today and if all good I'm happy to add myself as the maintainer of this.