patch 8.2.3320: some local functions are not static

Problem:    Some local functions are not static.
Solution:   Add "static".  Move snprintf() related code to strings.c.
            (Yegappan Lakshmanan, closes #8734)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index c071a7a..0f0e627 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -598,7 +598,7 @@
  * Execute the "+cmd" argument of "edit +cmd fname" and the like.
  * This allows for using a range without ":" in Vim9 script.
  */
-    int
+    static int
 do_cmd_argument(char_u *cmd)
 {
     return do_cmdline(cmd, NULL, NULL,