Fix unresolved symbols in problemreporter plugin

Fixes:
[kdevelop(28902)/(default)
KDevelop::PluginController::loadPluginInternal(526): Can't load plugin
"kdevproblemreporter" because a factory to load the plugin could not be
obtained: "Cannot load library
/home/kfunk/devel/install/kf5-stable/lib/x86_64-linux-gnu/plugins/kdevplatform/25/kdevproblemreporter.so:
(/home/kfunk/devel/install/kf5-stable/lib/x86_64-linux-gnu/plugins/kdevplatform/25/kdevproblemreporter.so:
undefined symbol: _ZTIN8KDevelop18WatchedDocumentSetE)"

Not sure why this is popping up now...