[PATCH] Refactor parseFile API to use LinkerInput directly

[Shankar Kalpathi Easwaran]

  The problem with that being parseFile and readFile interface need to be changed back to MemoryBuffers when the LinkerInput class gets removed.

  I think as a first move, we should move the LinkerInput functionalities to FileNode.

http://llvm-reviews.chandlerc.com/D1598