Pass --enable-kde5 to autogen.sh to enable this feature. Then
add kde5 to the list of externals to link against KF5. I will
introduce other code that depends on KF5 though which will
leverage this feature.

Change-Id: I17e434a53ac769000b0f805b1f41cdc5c2c84ee2
Reviewed-on: https://gerrit.libreoffice.org/47715Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>