[llvm] [AMDGPU] Make globally-addressable-scratch opt-in (PR #189555)

[Pierre van Houtryve via llvm-commits]

Pierre-vh wrote:

* **#189556** <a href="https://app.graphite.com/github/pr/llvm/llvm-project/189556?utm_source=stack-comment-icon" target="_blank"><img src="https://static.graphite.dev/graphite-32x32-black.png" alt="Graphite" width="10px" height="10px"/></a>
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* `main`


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https://github.com/llvm/llvm-project/pull/189555