Fix KDE CI compile issue

Imported target "KF5::DocTools" includes non-existent path
"/home/jenkins/workspace/Frameworks kdoctools kf5-qt5 SUSEQt5.10/build/src"
in its INTERFACE_INCLUDE_DIRECTORIES.

Reuse of target file generated with 'export(EXPORT ...' for installing does
not work because it contains local build pathes.

Fixup of commit 0bf3f34.

CCMAIL: luigi.toscano@tiscali.it