The compiled dtd's are currently built by hand.  Currently, something like
the following will work:

../../src/xemacs -batch -q -l psgml-parse.elc -l psgml-dtd.elc -eval "(progn (sgml-set-global) (setq sgml-no-elements 0) (sgml-compile-dtd \"$(pwd)/html.dtd\" \"$(pwd)/cdtd/html\" []))"

Note that the parameters are taken roughly from the ECAT file.