Disable unused GWKRoundValueT and GWKClampValueT (#5790)

git-svn-id: https://svn.osgeo.org/gdal/trunk@28226 f0d54148-0727-0410-94bb-9a71ac55c965
ifdef HAVE_EXPAT for fields only used when compiled with expat

git-svn-id: https://svn.osgeo.org/gdal/trunk@28227 f0d54148-0727-0410-94bb-9a71ac55c965