Fix compilation issue while xml is disabled

src/variables/xml.cc

@@ -21,11 +21,13 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
+#ifdef WITH_LIBXML2
 #include <libxml/xmlschemas.h>
 #include <libxml/xpath.h>
 #include <libxml/tree.h>
 #include <libxml/parser.h>
 #include <libxml/xpathInternals.h>
+#endif
 
 #include <iostream>
 #include <string>
@@ -44,6 +46,12 @@
 namespace modsecurity {
 namespace Variables {
 
+#ifndef WITH_LIBXML2
+void XML::evaluate(Transaction *t,
+    Rule *rule,
+    std::vector<const VariableValue *> *l) { }
+#else
+
 void XML::evaluate(Transaction *t,
     Rule *rule,
     std::vector<const VariableValue *> *l) {
@@ -138,6 +146,7 @@ void XML::evaluate(Transaction *t,
     xmlXPathFreeContext(xpathCtx);
 }
 
+#endif
 
 }  // namespace Variables
 }  // namespace modsecurity