Fixed compile against libxml2 2.12

Quote from Fedora mailing lists:

The latest released versions of libxml2 have a couple of important
changes in header files that have unintentionally caused some packages
to fail to build without modification, including:

* several functions now accept or return a const xmlError struct
* cyclic dependencies in header files were fixed (by dropping some includes)

2 files changed, 22 insertions, 23 deletions

diff --git a/src/utils/xml.cpp b/src/utils/xml.cpp
index fea5589f..252a9bd2 100644
--- a/src/utils/xml.cpp
+++ b/src/utils/xml.cpp
@@ -21,10 +21,6 @@
 
 #include "utils/xml.h"
 
-#include <iostream>
-#include <fstream>
-#include <cstring>
-
 #include <libxml/parser.h>
 #include <libxml/xmlerror.h>
 
@@ -37,14 +33,33 @@
 
 namespace XML
 {
-    static void xmlLogger(void *ctx, xmlErrorPtr error);
-
     struct XMLContext
     {
         std::string file;
         bool resman;
     };
 
+#if LIBXML_VERSION >= 21200
+    static void xmlLogger(void *ctx, const xmlError *error)
+#else
+    static void xmlLogger(void *ctx, xmlErrorPtr error)
+#endif
+    {
+        auto *context = static_cast<XMLContext*>(ctx);
+
+        if (context)
+            logger->log("Error in XML file '%s' on line %d",
+                        context->file.c_str(), error->line);
+        else
+            logger->log("Error in unknown xml file on line %d",
+                        error->line);
+
+        logger->log("%s", error->message);
+
+        // No need to keep errors around
+        xmlCtxtResetLastError(error->ctxt);
+    }
+
     Document::Document(const std::string &filename, bool useResman):
         mDoc(nullptr)
     {
@@ -160,23 +175,6 @@ namespace XML
         return nullptr;
     }
 
-    static void xmlLogger(void *ctx, xmlErrorPtr error)
-    {
-        auto *context = static_cast<XMLContext*>(ctx);
-
-        if (context)
-            logger->log("Error in XML file '%s' on line %d",
-                        context->file.c_str(), error->line);
-        else
-            logger->log("Error in unknown xml file on line %d",
-                        error->line);
-
-        logger->log("%s", error->message);
-
-        // No need to keep errors around
-        xmlCtxtResetLastError(error->ctxt);
-    }
-
     void init()
     {
         // Initialize libxml2 and check for potential ABI mismatches between
diff --git a/src/utils/xml.h b/src/utils/xml.h
index df8dd1bd..256a964b 100644
--- a/src/utils/xml.h
+++ b/src/utils/xml.h
@@ -22,6 +22,7 @@
 #ifndef XML_H
 #define XML_H
 
+#include <libxml/parser.h>
 #include <libxml/tree.h>
 
 #include <string>