[llvm] [SPIR-V] Emit builtin variable OpVariable into entry block (PR #189958)

[Arseniy Obolenskiy via llvm-commits]

aobolensk wrote:

> Fine for me. But should we added dedicated testing for this for both kernel and shader?

OpGroupAsyncCopy requires the Kernel capability. So I added generic tests.

That revealed that on another code path there is one more issue with the same root cause. Fixed that as well. Please, take a look 

https://github.com/llvm/llvm-project/pull/189958