[llvm] [BasicBlockUtils] Fix loopinfo header in split block before (PR #179408)

[Nikita Popov via llvm-commits]

nikic wrote:

This conflicts with other recent work on this function (see https://github.com/llvm/llvm-project/pull/179392 for latest version). Does that one fix your issue as well?

https://github.com/llvm/llvm-project/pull/179408