[clang] [clang-tools-extra] [llvm] [clang] Simplify device kernel attributes (PR #137882)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

1 set of questions, something I'm concerned about:  How do we make sure we don't try to have two kernel languages defined at the same time (I realize that might be messy, but it is something that could happen), then just are checking language version?

https://github.com/llvm/llvm-project/pull/137882