stdenv: fix nix develop

[wolfgangwalther]

This was introduced in #360466.

See #360466 (comment) for details.

Still building everything to check this actually works.

@trofi

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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[wolfgangwalther]

tests.stdenv are fine, nix develop -f. hello breaks before this commit and is fixed after. LGTM.

[philiptaron]

Hacks on hacks, but we did pick Bash as the language de guerre for stdenv. @Ma27 @wolfgangwalther do you think there's something we could do in Nix itself to make the original version work?

[Mic92]

@philiptaron NixOS/nix#11921

[roberth]

Reminds me that the nix develop/stdenv coupling is Very Bad.

• Tracking issue: Allow to get rid of nix develop "shell" logic nix#7501
• Would love some help with: [WIP] devShellTools.buildShellEnv #330822 (Nixpkgs committers can push)

(simplest root cause was NixOS/nix#11921, fwiw)