D9330: Fix cmake warning (with cmake >= 3.9.0)

[Laurent Montel]

mlaurent created this revision.
Restricted Application added a project: Frameworks.
Restricted Application added a subscriber: Frameworks.

TEST PLAN
  build

REPOSITORY
  R241 KIO

BRANCH
  fix_cmake_warning

REVISION DETAIL
  https://phabricator.kde.org/D9330

AFFECTED FILES
  CMakeLists.txt

To: mlaurent
Cc: #frameworks
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