[clang] [NFC][Clang] Add `setExprs` overload to reduce some code duplication (PR #139749)

[Erich Keane via cfe-commits]

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@@ -506,6 +506,14 @@ class OpenACCClauseWithExprs : public OpenACCClauseWithParams {
     Exprs = NewExprs;
   }
 
+  /// Used only for initialization, the leaf class can initialize this to
+  /// trailing storage, and initialize the data in the trailing storage as well.
+  void setExprs(MutableArrayRef<Expr *> NewExprs, ArrayRef<Expr *> Values) {
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erichkeane wrote:

```suggestion
  void setExprs(MutableArrayRef<Expr *> Storage, ArrayRef<Expr *> Exprs) {
```

Or something more like that?  

https://github.com/llvm/llvm-project/pull/139749