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

[Sven van Haastregt via cfe-commits]

svenvh wrote:

Echoing what Eli said: there isn't too much value in these tests.  The bulk of the core OpenCL builtins aren't tested in clang (as it would be too exhaustive); instead the OpenCL-CTS project covers that.  These vendor specific builtins may not be covered there though, so adding these tests here should be okay (provided they don't increase testing time significantly).

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