Poco can be built with ENABLE_UTIL=ON and ENABLE_XML=OFF, but use of Poco::Util requires Poco::XML
This fixes problems when a project adds a directory to CMAKE_PREFIX_PATH, then calls find_package(Poco ...) and afterwards calls find_package() for another project located in one of the directories of the original CMAKE_PREFIX_PATH variable.
The generated PocoConfig.cmake can be used by other CMake projects using find_package.