Motivation for this change

Qt 4 is old. Might also solve #21668.

I've also tried to compile it with Wine for plugin support, but haven't succeeded yet, requires 32-bit glibc.

By the way: v1.1.90 is also known as v1.2.0-rc1: https://github.com/LMMS/lmms/releases/tag/v1.1.90

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.