Plasma Workspace - Improperly exporting targets

[Ben Cooksley]

Hi Plasma Devs,

It would appear Plasma Workspace is improperly exporting it's targets,
leading to build failures. This particularly affects Apper, which is
unable to build on the CI system as a result. Please ensure when
exporting targets / finding libraries that the full path to the
library is given, not a short name.

Please see https://build.kde.org/job/apper%20master%20kf5-qt5/3/PLATFORM=Linux,compiler=gcc/consoleFull
for more details.

Thanks,
Ben