GCC9 requires upstream fix because of:
/wrkdirs/usr/ports/x11-themes/qtcurve-gtk2/work/qtcurve-a1ec5f8/.cmake_utils_base/cmake_c_macros/include_fix/qtcurve-utils/gtkprops.h:80:24: error: a reinterpret_cast is not a constant expression
80 | return (GObject*)qtcContainerOf(p, Props, name)->m_w; \ | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/wrkdirs/usr/ports/x11-themes/qtcurve-gtk2/work/qtcurve-a1ec5f8/.cmake_utils_base/cmake_c_macros/include_fix/qtcurve-utils/gtkprops.h:161:9: note: in expansion of macro 'DEF_WIDGET_SIG_CONN_PROPS'