bin/MitkWorkbench --BlueBerry.clean: org.blueberry.core.expressions fails to start because of missing symbol berry::SmartPointer<Expression> berry::ElementHandler::Create(ExpressionConverter* converter, Poco::XML::Element* element). However, this symbol seems to be exported when checking with readelf -Ws and it compares well to the Clang version.
bin/MitkWorkbench: We have some loose dependencies to Qt5PrintSupport that GCC 7.3 doesn't handle well when linking. Turns out that some dummy code right in those plugins that uses this library directly is a workaround.
There is also an error indicating that the system version of Qt is mixed with the actual version of Qt used when building MITK. This error vanishes into thin air when starting the Workbench again.