[llvm] [TableGen] Allow emitter callbacks to use `const RecordKeeper &` (PR #104716)

[Rahul Joshi via llvm-commits]

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@@ -24,29 +22,38 @@ class RecordKeeper;
 class raw_ostream;
 
 namespace TableGen::Emitter {
-using FnT = void (*)(RecordKeeper &Records, raw_ostream &OS);
-
-struct OptCreatorT {
-  static void *call();
-};
-
-extern ManagedStatic<cl::opt<FnT>, OptCreatorT> Action;
+// Support const and non-const forms of callback functions.
+using FnNonConstT = void (*)(RecordKeeper &Records, raw_ostream &OS);
+using FnConstT = void (*)(const RecordKeeper &Records, raw_ostream &OS);
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jurahul wrote:

This can actually be used to our advantage for eliminating the std::variant.

https://github.com/llvm/llvm-project/pull/104716