[llvm] [ADT] Add computeNumBuckets to DenseMap (NFC) (PR #168301)

[Sergei Barannikov via llvm-commits]

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@@ -556,7 +556,10 @@ class DenseMapBase : public DebugEpochBase {
     return llvm::make_range(getBuckets(), getBucketsEnd());
   }
 
-  void grow(unsigned AtLeast) { derived().grow(AtLeast); }
+  void grow(unsigned AtLeast) {
+    AtLeast = derived().computeNumBuckets(AtLeast);
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s-barannikov wrote:

```suggestion
    AtLeast = DerivedT::computeNumBuckets(AtLeast);
```

https://github.com/llvm/llvm-project/pull/168301