[PATCH] [lld][PECOFF] Add WinLinkDriver and PECOFFTargetInfo.

[kledzik at apple.com]

  LGTM.

  My only question is name PECOFF.  I don't do Windows development, so I'm familiar with how the terms are used in practice.  Is PE ever used alone?  Does it just refer to the final executable format?  Or to object files too?  Are there still platforms that use vanilla COFF for object files and will there be a need for lld's PECOFF reader to support vanilla COFF?  In other words, should the Reader be "COFF" and able to handle PE/COFF extensions?  And the Writer be "PE"?  Or is this Windows-only and thus PECOFFReader and PECOFFWriter?

http://llvm-reviews.chandlerc.com/D865