libdpkg: Move <config.h> and <compat.h> to the top of the flex file

Use the %top directive to force those includes to be the first in the
source code, so that the system correctly picks up desired features,
like LFS.

Prompted-by: Jonathan Nieder <jrnieder@gmail.com>

debian/changelog

@@ -1,5 +1,9 @@
 dpkg (1.16.2) UNRELEASED; urgency=low
 
+  [ Guillem Jover ]
+  * Move <config.h> and <compat.h> to the top of trigdeferred.l to properly
+    use the configured features and compat code.
+
   [ Updated man page translations ]
   * German (Helge Kreutzmann).
 

lib/dpkg/trigdeferred.l

@@ -32,11 +32,12 @@
 
 %x midline
 
-%{
-
+%top {
 #include <config.h>
 #include <compat.h>
+}
 
+%{
 #include <sys/stat.h>
 #include <sys/fcntl.h>