[llvm] [CFIFixup] Allow function prologues to span more than one basic block (PR #68984)

[Fangrui Song via llvm-commits]

https://github.com/MaskRay approved this pull request.

LGTM!

It might be useful to pre-commit the test and demonstrate how this patch repositions CFI_REMEMBER_STATE.

https://github.com/llvm/llvm-project/pull/68984