bug#21389: bogus diagnostic about unused lexical variable in eshell/time

[Paul Eggert <eggert@cs.ucla.edu>]

To reproduce the problem in a fresh build from Emacs master, do this:

touch lisp/eshell/em-unix.el
make

The output will include the following lines:

eshell/em-unix.el:933:1:Warning: Unused lexical variable ‘args’
eshell/em-unix.el:963:1:Warning: Unused lexical argument ‘args’

The first diagnostic is bogus.  The second one is correct.  Perhaps the 
byte compiler is getting confused by the second one and the confusion is 
affecting the first one.

The first diagnostic is generated for code that starts off like this:

(defun eshell/time (&rest args)
   "Implementation of \"time\" in Lisp."
   (let ((time-args (copy-alist args))
      ...

so the lexical variable ‘args’ is being used.