I just installed Xcode version 4.3.1 and I get this error:
libxml / tree.h file not found
I have also installed Xcode 4.2, and
LibXML2 library solved
SOLUTION!
if you have xcode 4.3.x in /Application
need ONLY add: "/usr/include/libxml2" without quote in Application TARGET -> Header search path.
for this -> double click on the line -> on little window click plus sign an write /usr/include/libxml2
nb - need also add libxml2.dylib to the framework. I use 2.2.7.3
hope help you