D5741: Fix test when compiling from a tarball

[Harald Sitter]

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

REPOSITORY
  R240 Extra CMake Modules

BRANCH
  master

REVISION DETAIL
  https://phabricator.kde.org/D5741

To: apol, #frameworks, joselema, sitter
Cc: #build_system