Fixed the Xcode project building of LLVM to be a bit more user friendly:

- If you download and build the sources in the Xcode project, x86_64 builds
  by default using the "llvm.zip" checkpointed LLVM.
- If you delete the "lldb/llvm.zip" and the "lldb/llvm" folder, and build the
  Xcode project will download the right LLVM sources and build them from 
  scratch
- If you have a "lldb/llvm" folder already that contains a "lldb/llvm/lib"
  directory, we will use the sources you have placed in the LLDB directory.
  
Python can now be disabled for platforms that don't support it. 

Changed the way the libllvmclang.a files get used. They now all get built into
arch specific directories and never get merged into universal binaries as this
was causing issues where you would have to go and delete the file if you wanted
to build an extra architecture slice.

llvm-svn: 143678