[clang] [llvm] [Offload][Driver] Split frontend CUDA/HIP language assumptions from backend device (PR #212373)

[Matt Arsenault via cfe-commits]

https://github.com/arsenm commented:

There are a lot of changes here, and not all of them seem to fit under the title (e.g., why are there any IR generation changes?), or eliminate language mode checks. Can this be broken down further 

https://github.com/llvm/llvm-project/pull/212373