[llvm] [SPIRV] Add explicit layout (PR #135789)

[Michal Paszkowski via llvm-commits]

michalpaszkowski wrote:

> @michalpaszkowski @MrSidims Any results from the CTS tests?

@s-perron Sorry, this took a bit longer than I anticipated, I found no regressions with OpenCL CTS. The change LGTM from my side. 

@asudarsa Would you be able to double-check with DPC++ CI?

https://github.com/llvm/llvm-project/pull/135789