[llvm] [AMDGPU] Add amdgpu-lower-exec-sync pass to lower named-barrier globals (PR #165692)

[Sameer Sahasrabuddhe via llvm-commits]

https://github.com/ssahasra approved this pull request.

LGTM. Just one nitpick, but not very important.

https://github.com/llvm/llvm-project/pull/165692