[clang] [Clang][AMDGPU] Stop defaulting to `one-as` for all atomic scopes (PR #120095)

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b-sumner wrote:

@JonChesterfield I think I agree with you.  And OpenCL source should not be calling builtins to begin with since they're not officially part of the OpenCL language.

https://github.com/llvm/llvm-project/pull/120095