[clang] [OpenCL][NFC] Expand test coverage for Intel OpenCL extension builtins (PR #199968)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic approved this pull request.

I'm not sure these tests are providing a lot of value; the compiler isn't even aware these functions exist.  This is basically just checking the function signatures in opencl-c.h.  That said, we probably do want some coverage so someone doesn't accidentally delete a function or something.

LGTM

https://github.com/llvm/llvm-project/pull/199968