This patch makes use of recently added relocation reference data. The bulk

of this is derived from the Mach-O writer.  Reviewed by: Nick Kledzik.
 * Adds loop to SectionChunk::write traverse references calling the
   writer's fixup handler, applyFixup.
 * Adds method, ELFWriter::buildAtomToAddressMap to that creates a
   mapping from an atom to its runtime address.
 * Adds method, ELFWriter::addressOfAtom to return the runtime address
   of the atom. 

llvm-svn: 164618