[PATCH] [lld] Move AtomLayout from ELF to Core so that it can be used by non-ELF writers.

[Rui Ueyama]

  Michael,

  Currently AtomLayout has an object of Atom. Do you think we should change the type to DefinedAtom? My understanding is that atoms that will be layout are only defined ones. Undefined or external atoms does not have contents and does not occupy bytes in segments. So it feel an AtomLayout should only have a pointer to DefinedAtom. That change would eliminate some dyn_cast from our code.

http://llvm-reviews.chandlerc.com/D977