python3Packages.pyvex: fix cross

[SFrijters]

Tested with nix build .#pkgsCross.aarch64-multiplatform.python3Packages.pyvex.

I've also tested this change at runtime by cross-compiling a Python env with this package, copying the closure to a Raspberry Pi 4, and importing the module on the Raspberry Pi. The build machine is x86_64 and binfmt is disabled (checked by trying to run the cross-compiled environment, and I correctly got "cannot execute binary file: Exec format error"). nix path-info -r ./result | grep -v aarch returns no results so it looks clean to me.

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/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 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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