patch 8.2.3271: Vim9: cannot use :command or :au with block in :def function

Problem:    Vim9: cannot use :command or :au with a block in a :def function.
Solution:   Recognize the start of the block.

src/ex_docmd.c

@@ -2741,7 +2741,7 @@ checkforcmd(
  * Check for an Ex command with optional tail, not followed by "(".
  * If there is a match advance "pp" to the argument and return TRUE.
  */
-    static int
+    int
 checkforcmd_noparen(
     char_u	**pp,		// start of command
     char	*cmd,		// name of command