[clang] [llvm] [NVPTX][Draft] Make `__nvvm_nanosleep` a no-op if unsupported (PR #81033)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

Okay, `__nvvm_reflect` doesn't work fully here because the `nanosleep` builtin I added requires `sm_70` at the clang level. Either means I'd need to go back to inline assembly or remove that requirement at least from clang so it's a backend failure.

https://github.com/llvm/llvm-project/pull/81033