Error trying to build tramp 2.1.18-pre with GNU Emacs 21.3

[skip]

I just learned that our GNU Emacs installation doesn't have tramp (I'm
mostly an XEmacs user), so I downloaded the latest version via CVS and set
to work.  I configured it like so:

    ./configure --prefix=/opt/app/emacs-21.3 --with-emacs=emacs

then ran make which gave this error output:

    emacs --no-site-file -batch --eval "(add-to-list 'load-path \".\")" -f 
batch-byte-compile tramp.el
    Loading 
/opt/app/emacs-21.3/libexec/emacs/21.3/i386-pc-solaris2.8/fns-21.3.1.el 
(source)...
    While compiling toplevel forms in file 
/home/titan/skipm/emacs/tramp/lisp/tramp.el:
      !! Wrong number of arguments ((#<subr featurep> 2))
    Done
    make[1]: *** [tramp.elc] Error 1

The INSTALL file indicates that tramp should work with GNU Emacs 21.  A
quick Google for "emacs tramp wrong number of arguments" turned up some old
problems, but nothing which looked like this.  I tried byte compiling
tramp.el interactively hoping it would give slightly more detail, but it
didn't.

Looking at the calls to (featurep) in tramp.el I don't see any which call it
with two arguments.  I'm open to suggestions about where to dig further for
the cause of this error.  (Any idea how to get byte-compile to give me a
line number?)

Thx,

-- 
Skip Montanaro - address@hidden - http://www.smontanaro.net/