qtxmlpatterns doesn't build on gcc 7.2

/home/rutledge/dev/qt56/qtxmlpatterns/src/xmlpatterns/parser/qxslttokenizer.cpp: In member function ‘void QPatternist::XSLTTokenizer::queueSorting(bool, QPatternist::TokenSource::Queue*, bool)’:
/home/rutledge/dev/qt56/qtxmlpatterns/src/xmlpatterns/parser/qxslttokenizer.cpp:2637:69: error: enum constant in boolean context [-Werror=int-in-bool-context]
                 if(QXmlStreamReader::Characters && whitespaceToSkip())
                                                                     ^