[PATCH] [mach-o] Reader first steps, yaml support

[kledzik at apple.com]

  Sean,  yes, I had thought about that.  The problem is the intermediate "normalized mach-o" data structure.  yaml2obj goes straight from yaml text to a binary obj.  I want half steps that I can mix and match.

  The intermediate in-memory format is also why this is unit test based and not lit based.  I'm testing the in-memory representation.

  I can see the value of moving this down into llvm's Object stuff.  But I would kinda like to get it all working first.

http://llvm-reviews.chandlerc.com/D1276