[clang] [CIR][CUDA] Upstream device stub body emission and name mangling (PR #177790)

[David Rivera via cfe-commits]

RiverDave wrote:

> There is an awful lot of code in the CUDA runtime class that isn't covered by the tests. Can you stub it out until it's needed?

Thanks for the feedback yet again. I've made sure that `kernel-call.cu` has enough coverage for CUDA at least. as @koparasy stated the current implementation likely works for HIP, nonetheless I've added assertions when compiling against it. We can remove those once we land enough test coverage.

https://github.com/llvm/llvm-project/pull/177790