[PATCH] [lld] add calls to nativereader/nativewriter

[kledzik at apple.com]

  Then MutableFile could have a method which takes a File and replaces all its atoms with atoms from the new file, as well as any File level attributes.  It is not clear to me who should own the File parameter when this method is done.  We need it to live on because it may own the mapped memory being used by some of the atoms.

http://llvm-reviews.chandlerc.com/D1955