Qt is configured with rather long configure:
and then built and installed. Now, running any application fails with qt.qpa.plugin: Could not find the Qt platform plugin "windows" in "". And after that is manually fixed by adding plugin directory with QCoreApplication::addLibraryPath(), then all Qt Quick applications complain about missing Qt Quick imports. Again, setting QML2_IMPORT_PATH manually fixes the problem.
If we print the QCoreApplication::libraryPaths() before QApplication is created, it is empty. Debugging the function shows that installPathPlugins = QLibraryInfo::location(QLibraryInfo::PluginsPath); contains correct path, but QFile::exists() returns false for it.
This problem has been reproduced on Windows 7 and 10 with MinGW 64bit and on Linux with the above configuration.