This removes a bunch of llvm_unreachables and makes a File's mutability part of the type system.

llvm-svn: 172297

  * Moves enum Scope from DefinedAtom.h to Atom.h
  * Adds scope method to AbsoluteAtom class
  * Updates YAML to print scope of AbsoluteAtoms
  * Update Native Reader/Writer to handle this new, "attribute"
  * Adds testcase 
Reviewed and approved by Nick Kledzik

llvm-svn: 166189

llvm-svn: 163573

llvm-svn: 160740

llvm-svn: 160370

put the public function createReaderPECOFF() in the lld namespace and everything else in is own namespace

llvm-svn: 158135

llvm-svn: 158134

now Reader and Writer subclasses for each file format.  Each Reader and
Writer subclass defines an "options" class which controls how that Reader
or Writer operates.

llvm-svn: 157774

llvm-svn: 156130

There are no tests for this yet because I still need to finish the
YAML -> COFF converter so we don't get binary files checked in.

llvm-svn: 156100