stop spewing libxml2 warnings during filter detection

Change-Id: Ifef3e75065e55aefba0f9498cf517efaf78ba6c1

external/libetonyek/UnpackedTarball_libetonyek.mk

@@ -17,6 +17,7 @@ $(eval $(call gb_UnpackedTarball_add_patches,libetonyek,\
 	external/libetonyek/win_build.patch.1 \
 	external/libetonyek/ubsan.patch \
 	external/libetonyek/rpath.patch \
+	external/libetonyek/silence-libxml.patch \
 	external/libetonyek/0001-fix-brain-fart.patch.1 \
 ))
 

external/libetonyek/silence-libxml.patch

+--- src/lib/EtonyekDocument.cpp
++++ src/lib/EtonyekDocument.cpp
+@@ -103,12 +103,21 @@
+   return false;
+ }
+ 
++namespace
++{
++  void handleError(void * /*arg*/, const char * /*msg*/, xmlParserSeverities /*severity*/, xmlTextReaderLocatorPtr /*locator*/)
++  {
++  }
++}
++
+ bool probeXML(DetectionInfo &info)
+ {
+   const shared_ptr<xmlTextReader> reader(xmlReaderForIO(readFromStream, closeStream, info.m_input.get(), "", 0, 0), xmlFreeTextReader);
+   if (!reader)
+     return false;
+ 
++  xmlTextReaderSetErrorHandler(reader.get(), handleError, NULL);
++
+   int ret = 0;
+   do
+   {