Build for example sql plugin static. Try to add the static plugin as build-in to dynamic application using QTPLUGIN += qsqlite. Link does not happen statically, you must replace QTPLUGIN with LIBS.

Quote from qmake Variable Reference -documentation:
QTPLUGIN
This variable contains a list of names of static plugins that are to be compiled with an application so that they are available as built-in resources.

Fix either documentation or QTPLUGIN option.