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

[Steven Perron via cfe-commits]

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

I believe changes like this (I did not test my suggestions) will remove the linkage error by making the function entry points.

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