autoload org-babel-tangle-lang-exts from ob-tangle

* lisp/ob-tangle.el: autoload org-babel-tangle-lang-exts from ob-tangle

lisp/ob-tangle.el

@@ -37,6 +37,7 @@
 (declare-function org-back-to-heading "org" (invisible-ok))
 (declare-function org-fill-template "org" (template alist))
 
+;;;###autoload
 (defcustom org-babel-tangle-lang-exts
   '(("emacs-lisp" . "el"))
   "Alist mapping languages to their file extensions.