D6992: Fix build on Linux without X11

[Volker Krause]

vkrause added a task: T6924: Fix KF5 compilation without X11.

REPOSITORY
  R285 KCrash

REVISION DETAIL
  https://phabricator.kde.org/D6992

To: vkrause, #frameworks, bshah, graesslin
Cc: dfaure, graesslin, bshah