[clang] [SYCL] The sycl_kernel_entry_point attribute. (PR #111389)

[Tom Honermann via cfe-commits]

tahonermann wrote:

@erichkeane, I believe all of the concerns you raised have been resolved with the exception of the `constexpr` question for which you asked @keryell to weigh in. I hope we're close to consensus on no need for a change for that one. Please re-review when time permits.

https://github.com/llvm/llvm-project/pull/111389