Windows: Fix stdint.h redefinition warnings

We must include the headers, particulary stdint.h, at the top of
scanner.l so that the stdint.h defintions precede flex's own
replacements.

epan/dfilter/scanner.l

@@ -1,6 +1,14 @@
 %top {
 /* Include this before everything else, for various large-file definitions */
 #include "config.h"
+
+#include <stdlib.h>
+#include <errno.h>
+
+#include "dfilter-int.h"
+#include "syntax-tree.h"
+#include "grammar.h"
+#include "dfunctions.h"
 }
 
 /*
@@ -61,14 +69,6 @@
  * SPDX-License-Identifier: GPL-2.0-or-later
  */
 
-#include <stdlib.h>
-#include <errno.h>
-
-#include "dfilter-int.h"
-#include "syntax-tree.h"
-#include "grammar.h"
-#include "dfunctions.h"
-
 /*
  * Disable diagnostics in the code generated by Flex.
  */