[llvm] [APFloat] add power (PR #122889)

[Jakub Kuderski via llvm-commits]

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@@ -1536,6 +1536,27 @@ inline APFloat abs(APFloat X) {
   return X;
 }
 
+/// Returns X^N for N >= 0.
+/// Returns X^N for N >= 0.
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kuhar wrote:

```suggestion
```

https://github.com/llvm/llvm-project/pull/122889