Qt Lighthouse build gives runtime error with the xcb plugin

./mainwindow: symbol lookup error: /home/matthew/dev/qt5-refactor/qtbase/plugins/platforms/libxcb.so: undefined symbol: _ZN25QIBusPlatformInputContextC1Ev

The runtime dependency on QIBusPlatformInputContext::QIBusPlatformInputContext() appears not have been resolved by a modification to xcb.pro to allow the xcb plugin to be built without DBus support:

commit 32b54d58bde5aca89058caaf0d972e8d6ac1e97f

This commit allows the xcb plugin to be build but now results in the runtime error.

To reproduce,

qtbase built from the refactor branch at #32b54d5

Run one of the GUI examples with -platform xcb

Configure line: -nokia-developer -nomake examples -nomake demos -nomake tests -no-qt3support
-no-svg -no-xmlpatterns -no-webkit -qpa -confirm-license -no-dbus