[compiler-rt] [NFC] Make RingBuffer an atomic pointer (PR #82547)

[via llvm-commits]

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@@ -1061,16 +1064,29 @@ class Allocator {
       atomic_u32 DeallocationTrace;
       atomic_u32 DeallocationTid;
     };
-
+    StackDepot *Depot = nullptr;
+    uptr StackDepotSize = 0;
+    MemMapT RawRingBufferMap;
+    MemMapT RawStackDepotMap;
+    u32 RingBufferElements;
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ChiaHungDuan wrote:

```suggestion
    u32 RingBufferElements = 0;
```

https://github.com/llvm/llvm-project/pull/82547