This is a bit ugly.  Right now, I've got a prototype zsh-dev which
contains the following.

/usr/include/zsh:
builtin.epro    init.epro      mem.epro      sigcount.h     utils.epro
compat.epro     input.epro     module.epro   signals.epro   watch.epro
cond.epro       jobs.epro      options.epro  signals.h      zsh.h
exec.epro       lex.epro       params.epro   signames.epro  ztype.h
glob.epro       linklist.epro  parse.epro    string.epro
hashtable.epro  loop.epro      pattern.epro  subst.epro
hashtable.h     main.epro      prompt.epro   system.h
hist.epro       math.epro      prototypes.h  text.epro

/usr/share/zsh-dev:
makepro.awk

All of those are copied unchanged from the object directory of a
successful build of zsh.

For a proof-of-concept, I've adapted a little utility which reads an Ogg
Vorbis file and outputs its length in seconds and the comments/tags.

I've only tried it on one platform, but it works for me.  Beyond the
autotools (and other) sloppiness, probably the most objectionable thing
is that I've copied config.h and zsh.mdh from the zsh build dir.
config.h is pristine, but zsh.mdh is edited to cope with path changes
and to add vorbis.mdh.  vorbis.mdh is example.mdh copied and passed
through a search&replace.

I'm attaching the tarball in case anyone wants to see.  It's currently
necessary to hand-force -I/usr/include/zsh into CPPFLAGS.