[libxml2] Fix include order in c14n.h

[Nick Wellnhofer <nwellnhof src gnome org>]

commit fb08d9fe837ab64934e6ddc66d442e599c805ca4
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Sat Mar 20 22:02:26 2021 +0100

    Fix include order in c14n.h
    
    - Include xmlversion.h before testing feature flags.
    - Include libxml headers before extern "C".
    
    Fixes #226.

 include/libxml/c14n.h | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)
---
diff --git a/include/libxml/c14n.h b/include/libxml/c14n.h
index d74847df..af93de63 100644
--- a/include/libxml/c14n.h
+++ b/include/libxml/c14n.h
@@ -16,17 +16,19 @@
  */
 #ifndef __XML_C14N_H__
 #define __XML_C14N_H__
+
+#include <libxml/xmlversion.h>
+
 #ifdef LIBXML_C14N_ENABLED
 #ifdef LIBXML_OUTPUT_ENABLED
 
+#include <libxml/tree.h>
+#include <libxml/xpath.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif /* __cplusplus */
 
-#include <libxml/xmlversion.h>
-#include <libxml/tree.h>
-#include <libxml/xpath.h>
-
 /*
  * XML Canonicalization
  * http://www.w3.org/TR/xml-c14n