[PATCH] [lld][ELF] Add explictly exported atoms and export R_*_COPY'ed atoms.

[Shankar Kalpathi Easwaran]

  Any exported symbols would be seen by the runtime loader for symbol resolution. The loader keeps the symbols that it can resolve in a dynamic symbol table.

  This attribute may also appear in the object files.

  a) A hidden symbol should not appear in the dynamic symbol table.
  b) A protected symbol may not appear in the dynamic symbol table.

  Symbol export could also appear using declspec attributes too(http://gcc.gnu.org/wiki/Visibility)

  This would be associated with Symbol Visibility.

http://llvm-reviews.chandlerc.com/D1799