Building examples without widgets fails

make[2]: Entering directory `/tmp/e2/build/build/qtquickcontrols2/examples'
cd quickcontrols2/ && ( test -e Makefile || /tmp/e2/build/build/qtbase/bin/qmake -o Makefile /tmp/e2/build/qt-everywhere-opensource-src-5.9.2/qtquickcontrols2/examples/quickcontrols2/quickcontrols2.pro ) && make -f Makefile 
make[3]: Entering directory `/tmp/e2/build/build/qtquickcontrols2/examples/quickcontrols2'
cd gallery/ && ( test -e Makefile || /tmp/e2/build/build/qtbase/bin/qmake -o Makefile /tmp/e2/build/qt-everywhere-opensource-src-5.9.2/qtquickcontrols2/examples/quickcontrols2/gallery/gallery.pro ) && make -f Makefile 
cd chattutorial/ && ( test -e Makefile || /tmp/e2/build/build/qtbase/bin/qmake -o Makefile /tmp/e2/build/qt-everywhere-opensource-src-5.9.2/qtquickcontrols2/examples/quickcontrols2/chattutorial/chattutorial.pro ) && make -f Makefile 
cd sidepanel/ && ( test -e Makefile || /tmp/e2/build/build/qtbase/bin/qmake -o Makefile /tmp/e2/build/qt-everywhere-opensource-src-5.9.2/qtquickcontrols2/examples/quickcontrols2/sidepanel/sidepanel.pro ) && make -f Makefile 
cd texteditor/ && ( test -e Makefile || /tmp/e2/build/build/qtbase/bin/qmake -o Makefile /tmp/e2/build/qt-everywhere-opensource-src-5.9.2/qtquickcontrols2/examples/quickcontrols2/texteditor/texteditor.pro ) && make -f Makefile 
cd swipetoremove/ && ( test -e Makefile || /tmp/e2/build/build/qtbase/bin/qmake -o Makefile /tmp/e2/build/qt-everywhere-opensource-src-5.9.2/qtquickcontrols2/examples/quickcontrols2/swipetoremove/swipetoremove.pro ) && make -f Makefile 
cd contactlist/ && ( test -e Makefile || /tmp/e2/build/build/qtbase/bin/qmake -o Makefile /tmp/e2/build/qt-everywhere-opensource-src-5.9.2/qtquickcontrols2/examples/quickcontrols2/contactlist/contactlist.pro ) && make -f Makefile 
cd flatstyle/ && ( test -e Makefile || /tmp/e2/build/build/qtbase/bin/qmake -o Makefile /tmp/e2/build/qt-everywhere-opensource-src-5.9.2/qtquickcontrols2/examples/quickcontrols2/flatstyle/flatstyle.pro ) && make -f Makefile 
cd wearable/ && ( test -e Makefile || /tmp/e2/build/build/qtbase/bin/qmake -o Makefile /tmp/e2/build/qt-everywhere-opensource-src-5.9.2/qtquickcontrols2/examples/quickcontrols2/wearable/wearable.pro ) && make -f Makefile 
Project ERROR: Unknown module(s) in QT: widgets
make[3]: *** [sub-flatstyle-make_first] Error 3