error compiling gwenhywfar for qt5

[Jack]

Under Gentoo, the ebuild for gwenhywfar-4.15.3 did not have any  
reference to qt5, which is clearly needed for KDE Frameworks.   
Including qt5 in the guis to be built looks good until compiling  
gui/qt5/qt5dialogbox.cpp which includes qt5dialogbox.hpp, which has a  
line "#include <QDialog>" which fails with "qt5dialogbox.hpp:16:19:  
fatal error: QDialog: No such file or directory".  QDialog is indeed  
present under /usr/lib/qt5/QTWidgets/ so I don't see why it shouldn't  
find it.

However, looking at the Makefile in the qt5 directory, I see a line
  qt4_includes = -I/usr/include/qt4 -I/usr/include/qt4/Qt  
-I/usr/include/qt4/QtCore -I/usr/include/qt4/QtGui
but no equivalent line for qt5.  I can't tell if this is something  
missing, or if qt5 has new ways of finding stuff.  I also don't believe  
I'm the first person to hit this issue, so I'm quite willing to believe  
it's some problem in my configuration.

Any suggestions?  Do I need to post to the gwenhywfar mailing list, or  
is there enough overlap with this list?

Jack