[llvm] [InstCombine][MemProf] Preserve !alloc_token metadata (PR #169242)

[Teresa Johnson via llvm-commits]

https://github.com/teresajohnson commented:

Hmm, looks like we are going to lose all MD, so this seems like a broader issue. Let me look and see if there are facilities for copying over all existing MD

https://github.com/llvm/llvm-project/pull/169242