[clang] [clang][SYCL Upstreaming] Add sycl_external attribute and restrict emitting device code (PR #140282)

[Mariya Podchishchaeva via cfe-commits]

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@@ -29,21 +29,10 @@ int foo() {
 }
 
 template <typename Name, typename Func>
-__attribute__((sycl_kernel)) void kernel_single_task(const Func &kernelFunc) {
+[[clang::sycl_external]] void kernel_single_task(const Func &kernelFunc) {
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Fznamznon wrote:

I think it was meant to be a kernel, so sycl_kernel_entry_point attribute would be appropriate here.
```suggestion
[[clang::sycl_kernel_entry_point]] void kernel_single_task(const Func &kernelFunc) {
```

https://github.com/llvm/llvm-project/pull/140282