This seems to be related to my problem building 21.2b13:
I configured without --mule, but:
Recompiling in /usr/local/src/i686-pc-linux-gnu/xemacs-21
with /usr/local/src/i686-pc-linux-gnu/xemacs-21/src/xemacs...
Cleaning out of date .elcs in directory `lisp'...
Cleaning out of date .elcs in directory `lisp'...done
Deleting .elc files without .el files...done.
Checking for Mule support...Yes <===============
Compiling files without .elc...