[clang] [libc][nfc] Include instantiations of gpuintrin.h in IR test case (PR #130956)

[Jon Chesterfield via cfe-commits]

JonChesterfield wrote:

Yep. I'm looking at changing their implementation and want a before&after shot in the git diff for the upcoming review. If that doesn't pan out, still good to get a heads up if codegen for these changes on us unexpectedly.

https://github.com/llvm/llvm-project/pull/130956