[llvm] Add unit test for CloneModule and #dbg_label (PR #91463)

[Stephen Tozer via llvm-commits]

https://github.com/SLTozer commented:

This largely LGTM at a glance - is there a reason for this to be in a separate PR to the patch that it depends on though? Normally we'd expect them to be merged in the same commit.

https://github.com/llvm/llvm-project/pull/91463