D23638: Fix build with cmake < 3.7

[Albert Astals Cid]

aacid accepted this revision.
This revision is now accepted and ready to land.

REPOSITORY
  R73 Rocs

REVISION DETAIL
  https://phabricator.kde.org/D23638

To: wbauer, #rocs, aacid
Cc: kde-edu, narvaez, apol
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