try to avoid the picking up of headers from a vendor Qt installation

kde-qt/kde-qt.spec

@@ -107,6 +107,7 @@ AutoReqProv:  no
         -xrender -no-xft -no-tablet -no-xkb \
         -disable-opengl -disable-sql \
         -no-exceptions -thread \
+        -I$QTDIR/include \
         %{l_cppflags} %{l_ldflags} \
         -I${l_x11_incdir} -L${l_x11_incdir} \
         -R%{l_prefix}/lib/kde