[clang] [llvm] [HIP] Support managed variables using the new driver (PR #123437)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Wonder if I should try really hard to update the struct we use for this before the branch in 8 days, since if it's default in CUDA now it'd break ABI for a release.

Can you implement the new path under a switch? 

https://github.com/llvm/llvm-project/pull/123437