[clang] [clang] Implement P2582R1: CTAD from inherited constructors (PR #98788)

[via cfe-commits]

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@@ -1960,24 +1960,38 @@ class ExplicitSpecifier {
 class CXXDeductionGuideDecl : public FunctionDecl {
   void anchor() override;
 
+public:
+  enum class SourceKind {
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cor3ntin wrote:

Can we get a better name / comment for this enum?

https://github.com/llvm/llvm-project/pull/98788