You may generate ui4.h and ui4.cpp parser files by using the generate_ui script
or manually by invoking the xsltproc command:

xsltproc generate_header.xsl ui4.xsd > ui4.h
xsltproc generate_impl.xsl ui4.xsd > ui4.cpp

Remember to update uic sources in qtbase module accordingly,
adapting the license.
