Fixed a case where we might end up trying to parse a type in the DWARF parser...

Fixed a case where we might end up trying to parse a type in the DWARF parser for a method whose class isn't currently in the process of completing itself. Currently, methods of a class, must be parsed when the class type that contains the method is asked to complete itself through the clang::ExternalASTSource virtual functions. Now we "do the right thing" by checking if the class is being defined, and if so we parse it, else we tell the class to complete itself so everything happens correctly.

llvm-svn: 141908