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

[Shankar Kalpathi Easwaran]

  could we add scopeGlobalHidden, anything that falls under scopeGlobal would be exported.

  All global defined atoms by default will have scopeGlobalHidden for executables.

  All global defined atoms by default will have scopeGlobal for shared libraries.

  Anything that needs to appear in the dynamic symbol table will change scope from scopeGlobalHidden to scopeGlobal (which makes it appear in the dynamic symbol table).

  This way there is no need to cast.

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