rust: build bpfel-unknown-none and bpfeb-unknown-none

[MisileLab]

this pull request based on (#373425 (comment)).
mitmproxy's new version(#373425) uses mitmproxy-rs, which uses -Zbuild-std=core for bpfel and bpfeb(https://github.com/mitmproxy/mitmproxy_rs/blob/79dbbf7e080574b7bb8b92766232f7e1b6e1d0a3/mitmproxy-linux/build.rs#L52-L62).

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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[alyssais]

This does not build.

[MisileLab]

This does not build.

rust only supports only no-std build for bpfel and bpfeb, I think that is reason that build failed.
ref: https://doc.rust-lang.org/nightly/rustc/platform-support.html#tier-3