[llvm] [AMDGPU] Only emit SCOPE_SYS global_wb (PR #110636)

[David Stuttard via llvm-commits]

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

Based on the internal discussion for this, I think this LGTM
Maybe get approval from one of the tagged reviewers though.

https://github.com/llvm/llvm-project/pull/110636