qtquickcontrols2/src/imports/platform/qquickplatformmessagedialog.cpp:379:51: error: use of overloaded operator '<<' is ambiguous

Building with clang5.0.2 on linux64 (ubuntu 14.04)

/home/build/Buildbot/qt5-analysis-linux64/source/qtquickcontrols2/src/imports/platform/qquickplatformmessagedialog.cpp:379:51: error: use of overloaded operator '<<' is ambiguous (with operand types 'QQmlInfo' and 'QPlatformDialogHelper::StandardButton')
default: qmlWarning(this) << "unknown button" << button; break;
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