QtSerialPort 5.3 cannot be compiled for Qt 4.x

The QtSerialPort documentation states that QtSerialPort can be built for Qt4. However, attempting to build the current 5.3 branch results in a link error:

libQtSerialPort.so: undefined reference to 'QSerialPort::dataErrorPolicyChanged(QSerialPort::DataErrorPolicy)'

I'm not entirely sure if this is a bug in the usual sense, or a documentation failure i.e. this branch is not expected to work and the doc fails to mention what branch should be built when targeting Qt4.

See also http://qt-project.org/forums/viewthread/47070/.