Wrong linker flags for static plugins with qmake

1. On Linux, create a static build of qtbase + qtdeclarative (developer build)
2. Use the qmake from that to build qtdeclarative/examples/quick/positioners

Expected:
The project compiles

Actual outcome:

/usr/bin/ld: cannot find -lQt6::QXcbIntegrationPlugin
/usr/bin/ld: cannot find -lQt6::QXcbEglIntegrationPlugin
...

For some reason, we try to link against the CMake target instead of the actual library