Qt6 needs patch?

[Jason Bacon <jtocino%gmx.com@localhost>]

I'll look into this when I get a change, assuming someone else doesn't
know the solution.  Seems NetBSD 9.3 has no C++ <filesystem> header, so

#include <QFileDialog>

generates the following error:

In file included from
/home/bacon/Pkgsrc/pkgsrc/wip/qmediamanager/work/.buildlink/qt6/include/QtCore/qdir.h:8:0,
                 from
/home/bacon/Pkgsrc/pkgsrc/wip/qmediamanager/work/.buildlink/qt6/include/QtWidgets/qfiledialog.h:8,
                 from
/home/bacon/Pkgsrc/pkgsrc/wip/qmediamanager/work/.buildlink/qt6/include/QtWidgets/QFileDialog:1,
                 from QShell.cpp:2:
/home/bacon/Pkgsrc/pkgsrc/wip/qmediamanager/work/.buildlink/qt6/include/QtCore/qfile.h:13:10:
fatal error: filesystem: No such file or directory
 #include <filesystem>
          ^~~~~~~~~~~~
compilation terminated.
*** [QShell.o] Error code 1

bmake: stopped in
/home/bacon/Pkgsrc/pkgsrc/wip/qmediamanager/work/qmediamanager-dcc06eb2bae989c24f17714948e39ce57f164dde
1 error