[PATCH] [lld][PECOFF] Implement the reader for the import library.

[kledzik at apple.com]

  Does this code instantiate a COFFDynamicAtom for every exported symbol in a .lib (DLL) which the Writer will later have to delete unused ones?  Or is there something that lazily instantiates COFFDynamicAtom as needed?

http://llvm-reviews.chandlerc.com/D987