[llvm] [llvm-jitlink] Add optional index argument in jitlink-check stub_addr() expressions (PR #78369)

[Stefan Gränitz via llvm-commits]

weliveindetail wrote:

A test that actually exercises the `index != 0` case will follow in https://github.com/llvm/llvm-project/pull/78371

https://github.com/llvm/llvm-project/pull/78369