fcitx-qt5: fix build with Qt 5.11

[mnacamura]

Motivation for this change

See fcitx/fcitx-qt5#34

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option 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.

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[Mic92]

Can you apply a patch with fetchpatch instead? fcitx/fcitx-qt5@af033e3

Then we know when to drop the patch on updates.

[mnacamura]

Changed it accordingly.

[Mic92]

Thanks!