#9267 fixed dropping of kernels by pynvjitlink by adding kernels to the @llvm.used list.

We also add global variables for representing an error handling state:

The variables seem to get optimized away when LTO is used with pynvjitlink, and I suspect they should also be added to the @llvm.used list to prevent them being optimized away - from the perspective of device code, they are only ever written to, so they look un-needed - it's only the host that looks up their values after kernel execution.