Unbreak after r436971.

kdelibs stopped setting several CMake policies to old values, as well as
setting an old minium required CMake version.

This causes the configuration stage to fail here, as libkvkontakte sets a
higher minimum required CMake version that sets the CMP0022 policy to NEW and
causes things to fail:

CMake Error in libkvkontakte/CMakeLists.txt:

Target "kvkontakte" has policy CMP0022 enabled, but also has old-style
LINK_INTERFACE_LIBRARIES properties populated, but it was exported without
the EXPORT_LINK_INTERFACE_LIBRARIES to export the old-style properties