[llvm-objcopy] Add support for visibility

I have no clue how this was missed when symbol table support was added. This
change ensures that the visibility of symbols is preserved by default.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@321681 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed