patch 8.2.3390: included xdiff code is outdated

Problem:    Included xdiff code is outdated.
Solution:   Sync with xdiff in git 2.33. (Christian Brabandt, closes #8431)
diff --git a/src/xdiff/xinclude.h b/src/xdiff/xinclude.h
index ad27d35..21ae35e 100644
--- a/src/xdiff/xinclude.h
+++ b/src/xdiff/xinclude.h
@@ -20,6 +20,8 @@
  *
  */
 
+// The following includes come from Vim:
+
 // defines HAVE_ATTRIBUTE_UNUSED
 #ifdef HAVE_CONFIG_H
 # ifdef VMS
@@ -44,6 +46,7 @@
 #if !defined(XINCLUDE_H)
 #define XINCLUDE_H
 
+// This effectively re-verts b46054b3746271d23feab0 from git
 #include <ctype.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -52,7 +55,10 @@
 #endif
 #include <string.h>
 #include <limits.h>
-
+// This include comes from git, so uncomment it
+#if 0
+#include "git-compat-util.h"
+#endif
 #include "xmacros.h"
 #include "xdiff.h"
 #include "xtypes.h"
@@ -62,4 +68,4 @@
 #include "xemit.h"
 
 
-#endif // #if !defined(XINCLUDE_H)
+#endif /* #if !defined(XINCLUDE_H) */