1) nuke ConstDataCoalSection, which is dead.
2) revise my previous patch for rdar://8018335,
  which was completely wrong.  Specifically, it doesn't 
  make sense to mark __TEXT,__const_coal as PURE_INSTRUCTIONS,
  because it is for readonly data.  templates (it turns out)
  go to const_coal_nt.  The real fix for rdar://8018335 was
  to give ConstTextCoalSection a section kind of ReadOnly 
  instead of Text.

llvm-svn: 112496