[llvm] [MergeFunctions] Add debug locations to redirected calls (PR #225625)

[Jeremy Morse via llvm-commits]

jmorse wrote:

Thanks for the details; I feel that a call that already doesn't have a source location is going to be extremely uncommon in a debug-info build, so it probably doesn't need too much consideration. There would be slightly-broken output even if MergeFunctions didn't run in that situation. So, probably no further action needed.

I think we'll have to address this in debug-info at some point due to the backtrace matter, but that's not relevant to this PR.

https://github.com/llvm/llvm-project/pull/225625