Filtering loaddefs files in lisp/Makefile

[Eli Zaretskii <eliz@gnu.org>]

What do people think about replacing this ugliness:

	    els=`echo $(lisptagsfiles1) $(lisptagsfiles2) $(lisptagsfiles3) $(lisptagsfiles4) | sed -e "s,$(lisp)/[^ ]*loaddefs[^ ]*,," -e "s,$(lisp)/ldefs-boot[^ ]*,,"`; \
	    ${ETAGS} -o $@ $$els

with a command that uses `find', e.g.:

	find . -name "*.el" -a -\! -( -name "*loaddefs.el" -o -name "ldefs-boot.el" -) | ${ETAGS} -o $@ -

The combined length of all the Lisp files expanded from
$(lisptagsfilesN) is 32K, so I guess a few shells will choke on what
we currently have, while doing it with `find' will avoid that problem.
As a bonus, we won't need to track the depth of the `lisp' tree
hierarchy by adding more of the $(lisptagsfilesN) variables.