bug#29400: 26.0; Add Elisp manual index entry for `defvar' to node `Compiler Errors'

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 24 Nov 2017 08:54:39 -0800 (PST)
> From: Drew Adams <drew.adams@oracle.com>
> Cc: 29400-done@debbugs.gnu.org
> 
> > but I don't understand why you wanted an
> > index entry with "defvar" in it.  A reader who will look for "defvar"
> > when they want to find ways of suppressing compiler warnings already
> > knows that defvar is used for that purpose, so why would they use such
> > a topic at Info-index's prompt?
> 
> To find exactly what the manual says about it.

But defvar is described elsewhere, and index entries about it should
lead there.  And after my changes, the description there mentions its
use for suppressing warnings, so I don't think an index entry leading
elsewhere is needed.

> Looking in the index for `warning' is not the only
> reasonable way to use an index for this - see above.

Feel free to suggest other topics, but "defvar" is definitely not one
of them.