ox: Ignore whitespace differences when resolving a radio link

* lisp/ox.el (org-export-resolve-radio-link): Ignore whitespace
  differences when resolving a radio link.
* testing/lisp/test-ox.el: Add test.

lisp/ox.el

@@ -4079,11 +4079,14 @@ INFO is a plist used as a communication channel.
 
 Return value can be a radio-target object or nil.  Assume LINK
 has type \"radio\"."
-  (let ((path (org-element-property :path link)))
+  (let ((path (replace-regexp-in-string
+	       "[ \r\t\n]+" " " (org-element-property :path link))))
     (org-element-map (plist-get info :parse-tree) 'radio-target
       (lambda (radio)
 	(and (eq (compare-strings
-		  (org-element-property :value radio) 0 nil path 0 nil t)
+		  (replace-regexp-in-string
+		   "[ \r\t\n]+" " " (org-element-property :value radio))
+		  nil nil path nil nil t)
 		 t)
 	     radio))
       info 'first-match)))

testing/lisp/test-ox.el

@@ -1719,7 +1719,15 @@ Another text. (ref:text)
 		(lambda (link)
 		  (org-element-property
 		   :value (org-export-resolve-radio-link link info)))
-		info))))))
+		info)))))
+  ;; Radio target is whitespace insensitive.
+  (should
+   (org-test-with-temp-text "<<<a radio>>> a\n  radio"
+     (org-update-radio-target-regexp)
+     (let* ((tree (org-element-parse-buffer))
+	    (info `(:parse-tree ,tree)))
+       (org-element-map tree 'link
+	 (lambda (link) (org-export-resolve-radio-link link info)) info t)))))