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

[Stephen Tozer via llvm-commits]

SLTozer wrote:

> Does the script handle exprloc `DW_AT_location`s (i.e., single location that implicitly covers the scope with no explicit range)?

No, although I _think_ that shouldn't be possible? I think we only emit that for constants or declares.

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