[clang] [clang][NFC] Refactor `Sema::TemplateDeductionResult` (PR #81398)

[Vlad Serebrennikov via cfe-commits]

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@@ -33,6 +33,7 @@ namespace clang {
 class Decl;
 struct DeducedPack;
 class Sema;
+enum class TemplateDeductionResult;
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Endilll wrote:

This is far from the first time we do unscoped enum → scoped enum refactoring so that we can forward declare enums. Me and @AaronBallman decided to stick to default `int` for scoped enums that are stored in bit-fieds. (This one is stored in bit-fields of width 8).

https://github.com/llvm/llvm-project/pull/81398