xcb plugin not installed even it was built

Build from git including xcb but both libqxcb.so and libQt5XcbQpa.so.5 were not installed and QtCreator did not run.

After copying plugin and lib into place QtCreator could be started.

git clone git://code.qt.io/qt/qt5.git
cd qt5/
git checkout 5.12
./init-repository --module-subset=default,-qtwebengine
rm -rf ../qt5-build # configure -recheck-all does not work
mkdir -p ../qt5-build
cd ../qt5-build
../qt5/configure -opensource -confirm-license -prefix /usr/local/bin/qt/5.12 -silent -nomake examples -nomake tests \
-skip qt3d -skip qtandroidextras -skip qtdatavis3d -skip qtlocation -skip qtmacextras -skip qtpurchasing -skip qtwinextras \
-xcb -xcb-xlib -qpa xcb
make -j$(grep -c ^processor /proc/cpuinfo)
sudo mkdir -p /usr/local/bin/qt/5.12
sudo make install

All required libs for build on debian were installed (incl. libxkbcommon-dev libxkbcommon-x11-dev)