[llvm] [ExtendLifetimes] Implement llvm.fake.use to extend variable lifetimes (PR #86149)

[Felipe de Azevedo Piovezan via llvm-commits]

felipepiovezan wrote:

I only skimmed the diff, but noticed there is no global isel lowering here. Were there any challenges in doing that or was it not considered?

https://github.com/llvm/llvm-project/pull/86149