ol: Fix info links with backquotes and backslashes

* lisp/ol.el (org-store-link): Remove spurious backslash appearing in
some Info buffers.

Reported-by: Achilles Yuce <ayuce@posteo.mx>
<http://lists.gnu.org/r/emacs-orgmode/2020-04/msg00405.html>

lisp/ol.el

@@ -1454,10 +1454,16 @@ non-nil."
 	  (org-link-store-props :type "calendar" :date cd)))
 
        ((eq major-mode 'help-mode)
-	(setq link (concat "help:" (save-excursion
-				     (goto-char (point-min))
-				     (looking-at "^[^ ]+")
-				     (match-string 0))))
+	(let ((symbol (replace-regexp-in-string
+		       ;; Help mode escapes backquotes and backslashes
+		       ;; before displaying them.  E.g., "`" appears
+		       ;; as "\'" for reasons.  Work around this.
+		       (rx "\\" (group (or "`" "\\"))) "\\1"
+		       (save-excursion
+			 (goto-char (point-min))
+			 (looking-at "^[^ ]+")
+			 (match-string 0)))))
+	  (setq link (concat "help:" symbol)))
 	(org-link-store-props :type "help"))
 
        ((eq major-mode 'w3-mode)