https://wiki.qt.io/Using_QString_Effectively
compile LabPlot with
add_definitions(
-DQT_USE_FAST_CONCATENATION -DQT_USE_FAST_OPERATOR_PLUS -DQT_NO_CAST_FROM_ASCII -DQT_NO_CAST_TO_ASCII -DQT_NO_CAST_FROM_BYTEARRAY -DQT_NO_URL_CAST_FROM_STRING -DQT_USE_QSTRINGBUILDER
)