Fix xcode project. 
Add missing files (lithium.cc, lithium.h, lithium-x64.cc). 
Add 64 bit targets to "All" targets group for Xcode build. 

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6239 ce2b1a6d-e550-0410-aec6-3dcde31c8c00