qt6.full: unlink qmake6

[wegank]

Description of changes

Closes #239971.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• 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/)
• 23.11 Release Notes (or backporting 23.05 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.

[Be-ing]

Thanks for the quick fix!

[vimpostor]

@wegank Was there a reason for applying this only to qt6.full?
The original downstream project that failed to build before this patch, now builds with qt6.full, but fails to build with the very same old issue when building with qt6.qtbase + qt6.qtdeclarative.

Shouldn't we apply this postBuild step for qt6.qtbase as well?

[wegank]

The point is that qmake6 doesn't work when called via symlink, which basically results in the following:

• Before this PR, ${qt6.full}/bin/qmake6 is a symlink to ${qt6.qtbase}/bin/qmake6: not OK.
• After this PR, ${qt6.full}/bin/qmake6 is a real file: OK.
• For your question, ${qt6.qtbase}/bin/qmake6 is a real file: OK. There's nothing to fix.

However, if you combine qt6.qtbase and qt6.qtdeclarative, you have to do the check yourself.

[vimpostor]

Thanks for clearing that up, makes sense. Although it is a bit cumbersome, that you then no longer can do a simple nix-shell -p qt6.qtbase qt6.qtdeclarative and have everything working.