[lld-macho] Extend lto-internalize-unnamed-addr.ll

* Test the case where a symbol is sometimes linkonce_odr and sometimes weak_odr
* Test the visibility of the symbols at the IR level, after the internalize
  stage of LTO is done. (Previously we only checked the visibility of
  symbols in the final output binary.)

Reviewed By: modimo

Differential Revision: https://reviews.llvm.org/D121428