[PATCH] [TargetInfo] Move LinkerInputFile to TargetInfo and rename more specific name

[Rui Ueyama]

  As to constness, we can avoid instantiating a SimpleFile with the "new" operator in addImplicitFiles() but instead making it a field. And then we can create an atom and add it to the file as addUndefinedSymbol() is called. addUndefinedSymbol() has side effect so it should be ok. With this design we can delete _undefinedSymbols from TargetInfo, so I think it's actually a cleaner than this patch.

http://llvm-reviews.chandlerc.com/D1016