Use "marblewidget" target again instead of var ${MARBLEWIDGET}
Summary:
It is just the targetname, use target property OUTPUT_NAME to control
the actual library name
Reviewers: rahn, sanjibanb, shentey, nienhueser, Marble
Reviewed By: nienhueser, Marble
Differential Revision: https://phabricator.kde.org/D2366