[llvm] [llvm-objcopy] Add llvm-objcopy option --set-visibility-sym (PR #80872)

[Fangrui Song via llvm-commits]

MaskRay wrote:

FWIW I filed https://sourceware.org/bugzilla/show_bug.cgi?id=31000 ("objcopy: add support for changing ELF symbol visibility") in 2023-10. While I think they will likely take an option to set the visibility (especially if someone sends a patch), there is some design space here. If `--set-symbol-flags` is present, then we might not need a special-purpose `--set-symbol-visibility`.

https://github.com/llvm/llvm-project/pull/80872