bug#27202: 26.0.50; Eldoc mode is broken

[Stephen Berman]

0. emacs -Q
1. M-: (car SPC
=> No function signature in the mode line, whereas before the breakage
   the mode line would display this:
   car: (LIST)

Git bisect says:

2349f1df1b11381c421287670ffd0f84725d7818 is the first bad commit
commit 2349f1df1b11381c421287670ffd0f84725d7818
Author: Dmitry Gutov <dgutov@yandex.ru>
Date:   Tue May 30 02:55:28 2017 +0300

    Turn global-eldoc-mode into a globalized minor mode
    
    * lisp/emacs-lisp/eldoc.el (global-eldoc-mode):
    Turn into globalized mode (bug#19853).
    (turn-on-eldoc-mode): Make it into a wrapper instead of alias.
    (eldoc-mode): Only show the message when called interactively.


In GNU Emacs 26.0.50 (build 36, x86_64-pc-linux-gnu, GTK+ Version 3.22.8)
 of 2017-06-01 built on rosalinde
Repository revision: 5dc0129c299f6cc7a0bdfbf7edc92a85bb3a0597
Windowing system distributor 'The X.Org Foundation', version 11.0.11901000

Configured using:
 'configure 'CFLAGS=-Og -g3''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
GTK3 X11

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix