- Hooked up deserialization of ObjCAtSynchronizedStmt Stmt::Create().

- Some minor optimizations of the encoding format for ObjCAtSynchronizedStmt.
- Reordered methods so that the deserialization methods for 
  ObjCAtSynchronizedStmt appear in alphabetical order with the corresponding
  methods of the other AST nodes.

llvm-svn: 46529