[ORC] Add default visibility to required JIT functions (#86322)

If you build LLVM with `-DCMAKE_CXX_VISIBILITY_PRESET=hidden` to help
reduce binary size, these symbols end up becoming local, and getting
stripped. This forces default visibility to override the global setting
in that case.

Relevant:
https://github.com/llvm/llvm-project/issues/62815#issuecomment-1560078260