iOS New VERSION of libxml2

I need at least version 2.2.23 of libxml2 because I am trying to use xmlSaveToBuffer function with XML_SAVE_NO_EMPTY flag so that the document doesn't print out empty tags.

What version is in the iphone? When I try to build is says that I am implicitly trying to define the function xmlSaveToBuffer at this line:

xmlSaveToBuffer(xmlbuffNew, NULL, XML_SAVE_NO_EMPTY);

I use the following imports:
#import <libxml/tree.h>
#import <libxml/parser.h>
#import <libxml/HTMLparser.h>
#import <libxml/xpath.h>
#import <libxml/xpathInternals.h>
#import <libxml/xmlsave.h>

Am I missing an import? or is the version of libxml too old?
If its too old.... how do I install the newest version in my iphone app???