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

[Tom Honermann via cfe-commits]

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+// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++17 -fsyntax-only -fsycl-is-device -verify %s
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tahonermann wrote:

Those tests are included with the diagnostic work that will be in the next PR. See [here](https://github.com/tahonermann/llvm-project/compare/sycl-upstream-fe-pr1...tahonermann:llvm-project:sycl-upstream-fe-pr2) for what has been completed. We still have some SFINAE issues to address (an invalid use of the attribute is triggering SFINAE and therefore affecting overload resolution) and I'm still working on a diagnostic for forward declarability of kernel names (for SYCL portability warnings; Clang won't actually require forward declarability since it won't depend on integration headers).

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