[clang] [llvm] [HLSL][DXIL][SPRIV] Added `GroupMemoryBarrier()` (PR #185383)

[Steven Perron via cfe-commits]

https://github.com/s-perron commented:

The SPIR-V code looks good. However, the Vulkan memory model chagnes the way barriers and atomics can be used. This code assumes it is not the vulkan memory model. We should have an assert for that.

https://github.com/llvm/llvm-project/pull/185383