[PATCH] [lld] Add basic linker script parsing.

[Michael Spencer]

  Yes, I intend for this to implement most of the linker script functionality. My plan is to produce an Atom that contains the section layout and other assorted info that doesn't effect resolving. Then add a LinkerScriptAtom that holds the expression for any atoms defined by the linker script with references to any symbols used by the expression.

http://llvm-reviews.chandlerc.com/D477