[llvm] [AMDGPU] Add target feature for waits before system scope stores. NFC. (PR #164993)

[Shilei Tian via llvm-commits]

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@@ -1466,6 +1466,12 @@ def FeatureClusters : SubtargetFeature< "clusters",
   "Has clusters of workgroups support"
 >;
 
+def FeatureWaitsBeforeSystemScopeStores
+    : SubtargetFeature<"waits-before-system-scope-stores",
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shiltian wrote:

nit: would be easier to read if one line per argument.

https://github.com/llvm/llvm-project/pull/164993