Describe the bug

A clear and concise description of what the bug is.

When a nixos configuration has nixpkgs.hostPlatform and nixpkgs.buildPlatform both set to the same string, the module defined here always determines that the system is cross-compiled, even when it should not be.

Steps To Reproduce

Steps to reproduce the behavior:

1. Make a nixos config with the example configuration:

{ nixpkgs.hostPlatform = "x86_64-linux"; nixpkgs.buildPlatform = "x86_64-linux"; }

3. Try building and notice that the entire world gets rebuilt since it tries to build cross-compilation toolchains

Expected behavior

A clear and concise description of what you expected to happen.

I would expect that the module would determine I am not cross-compiling the nixos system and build accordingly.

Screenshots

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Additional context

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Notify maintainers

Metadata

Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

[user@system:~]$ nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 6.6.8, NixOS, 24.05 (Uakari), 24.05.20231231.48d59d0`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.18.1`
 - nixpkgs: `/nix/store/4pxqlm2rwq6j6di78q178602jfnx2mys-source`

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