The majority of tests use QPluginLoader::setFileName implicitly, which
refuses to do any work in static builds. Therefore the majority of tests
are skipped. But in the future we'll get tests here that for example use
QPluginLoader::staticPlugins() and for that we want to include the
sub-directory in the build and test run.
Change-Id: Ib8ec274e22ac8050feaca8967eb8626b53876b92
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>