[llvm] [SelectionDAG] add cli option to write SelectionDAG graphviz to file (PR #161979)

[Matt Arsenault via llvm-commits]

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@@ -530,6 +530,9 @@ class SelectionDAG {
 
   /// Pop up a GraphViz/gv window with the DAG rendered using 'dot'.
   LLVM_ABI void viewGraph(const std::string &Title);
+  /// Pop up a GraphViz/gv window with the DAG rendered using 'dot', or write
+  /// the file out instead.
+  LLVM_ABI void viewGraph(const std::string &Title, const bool WriteFile);
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arsenm wrote:

```suggestion
  LLVM_ABI void viewGraph(const std::string &Title, bool WriteFile);
```
const does nothing here

https://github.com/llvm/llvm-project/pull/161979