[llvm] [AMDGPU][Offload] Enable memory manager use for up to ~3GB allocation size in omp_target_alloc (PR #151882)

[Joseph Huber via llvm-commits]

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@@ -1090,6 +1090,9 @@ struct GenericDeviceTy : public DeviceAllocatorTy {
   /// Pointer to the memory manager or nullptr if not available.
   MemoryManagerTy *MemoryManager;
 
+  /// Per device setting of MemoryManager's Threshold
+  virtual size_t getMemoryManagerSizeThreshold() { return 0 /* use default */; }
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jhuber6 wrote:

```suggestion
  virtual size_t getMemoryManagerSizeThreshold() { return 0; }
```

https://github.com/llvm/llvm-project/pull/151882