[llvm] [SPIR-V] Drop constant zero-sized memcpy/memmove/memset before selection (PR #201904)

[Arseniy Obolenskiy via llvm-commits]

aobolensk wrote:

> I have a feeling, that it might screw up something for HIP testing as we have few workarounds around zero-sized arrays, please run rocm-examples to see if the change regresses anything.

Hm, rocm-examples actually pass (cherry picked this patch on top of the https://github.com/ROCm/llvm-project, enables SPIR-V backend usage there and so on)

https://github.com/llvm/llvm-project/pull/201904