Refactor diagnostics for sycl_kernel_entry_point#48

Naghasan wants to merge 3 commits intotahonermann:sycl-upstream-fe-pr1tahonermann/llvm-project:sycl-upstream-fe-pr1from

Naghasan:sycl-upstream-fe-pr1-improved-diagsNaghasan/llvm-project:sycl-upstream-fe-pr1-improved-diagsCopy head branch name to clipboard