qmake uses single dash options; fixes error: "Failed call:...
qmake uses single dash options; fixes error: "Failed call: /usr/lib64/qt5/bin/qmake --query QT_INSTALL_PREFIX" when building against Qt6.
qmake uses single dash options; fixes error: "Failed call: /usr/lib64/qt5/bin/qmake --query QT_INSTALL_PREFIX" when building against Qt6.