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

[Paul T Robinson via llvm-commits]

pogo59 wrote:

There was also a [lightning talk at the 2017 US Dev Meeting](https://llvm.org/devmtg/2017-10/#lightning8). Our users have been happy with this feature for years.


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