[clang] [Headers] Create stub spirvintrin.h (PR #131164)

[Jon Chesterfield via cfe-commits]

JonChesterfield wrote:

@jhuber6 I think we should have this despite the rejected https://github.com/llvm/llvm-project/pull/131190.

Maybe we'll get some clang builtins for spirv. Otherwise some things can be done with the asm label hack. Some can just be left as nop, e.g. a suspend that does nothing. Regardless, this is the structure we want for the file, and it gives as a place to add functions incrementally as the corresponding reviews work themselves out.

https://github.com/llvm/llvm-project/pull/131164