My mistake. It was built without the floss patch, which already
incorporated in "Toggenburg."
From tarballs, floss and xfc patches by Andy Piper.
> XEmacs Build Report as generated
> by build-report-version 1.35 follows:
> Contents of /binary/xemacs-21.0-b46/Installation:
> (Output from most recent run of ./configure)
uname -a: CYGWIN32_NT DILBERT 4.0 19.1 i686 unknown
./configure '--site-includes=/usr/local/include'
XEmacs 21.0 "Toggenburg" configured for `i386-pc-cygwin32'.