hashlink: fix build with gcc-14

[paparodeo]

fixes: #368216

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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[lucasew]

nixpkgs-review result

Generated using nixpkgs-review.

Command: nixpkgs-review pr 369800

---

x86_64-linux

❌ 1 package failed to build:

• worldofgoo

✅ 2 packages built:

• hashlink
• megasync

[paparodeo]

nixpkgs-review result

Generated using nixpkgs-review.

Command: nixpkgs-review pr 369800

x86_64-linux

❌ 1 package failed to build:
✅ 2 packages built:

https://github.com/NixOS/nixpkgs/actions/runs/12564450512/attempts/1#summary-35027677217 only lists 1 rebuild and hashlink. this doesn't seem correct.

[lucasew]

This may be Mic92/nixpkgs-review#446

[paparodeo]

cc maintainers: @iblech @locallycompact @l0go