[clang] [llvm] [clang] Check validity of SYCL device target (PR #172366)

[Tom Honermann via cfe-commits]

https://github.com/tahonermann requested changes to this pull request.

Per discussion, it sounds like we'll postpone some of the changes. There is one change I would like to include with this PR if adding it doesn't cause other problems.

https://github.com/llvm/llvm-project/pull/172366