bug#31860: 27.0.50; make-process clears out eldoc-held echo area

[João Távora]

Hi,

$ ./emacs-master/src/emacs -Q

Eval in the scratch buffer

   (defun process-making-dummy-backend (report-fn &rest args)
     (make-process :name "dummy" :command '("echo"))
     (funcall report-fn nil))

   (setq flymake-diagnostic-functions '(process-making-dummy-backend))
    
   (flymake-mode)
    
Now start typing something like this
    
   (with-current-buffer

In Emacs 26.1 the arglist of with-current-buffer is displayed in the
mode-line.

In a recent master it is immediately cleared after the dummy flymake
handler kicks in, which is bug.  I think this started happening recently
but I dont have the time to bisect it.

João