A lot of people have problems with building LibreOffice on OS X Mountain Lion with latest Xcode 4.5.
Below you can see how I succeeded with it.
I tried building LibreOffice 126.96.36.199.
At first I tell you what you should NOT do to build LibreOffice.
Then you will see steps to build LibreOffice 188.8.131.52 on OS X 10.8 with Xcode 4.5.