[clang] [SYCL] Restrict the sycl_kernel_entry_point attribute spelling to C++11 style. (PR #151405)

[Erich Keane via cfe-commits]

https://github.com/erichkeane approved this pull request.

I think I saw a clang-format complaint, so make sure that +CI passes, else LGTM.

https://github.com/llvm/llvm-project/pull/151405