[llvm] [mlir] [polly] [IR] Only allow lifetime.start/end on allocas (PR #149310)

[William Moses via llvm-commits]

wsmoses wrote:

our use is a bit more complex than that, but for the time being I added a special vendored intrinsic (llvm.enzyme.lifetime_start/end), which we can use until upstream adds an intrinsic with the restored semantics: https://github.com/EnzymeAD/Enzyme/pull/2402/files

https://github.com/llvm/llvm-project/pull/149310