[NFC] AST: Define DenseMapInfo<KnownProtocolKind>.

Author: nate-chandler

include/swift/AST/KnownProtocols.h

@@ -71,4 +71,27 @@ void simple_display(llvm::raw_ostream &out,
 
 } // end namespace swift
 
+namespace llvm {
+template <typename T, typename Enable>
+struct DenseMapInfo;
+template <>
+struct DenseMapInfo<swift::KnownProtocolKind> {
+  using KnownProtocolKind = swift::KnownProtocolKind;
+  using Impl = DenseMapInfo<uint8_t>;
+  static inline KnownProtocolKind getEmptyKey() {
+    return (KnownProtocolKind)Impl::getEmptyKey();
+  }
+  static inline KnownProtocolKind getTombstoneKey() {
+    return (KnownProtocolKind)Impl::getTombstoneKey();
+  }
+  static unsigned getHashValue(const KnownProtocolKind &Val) {
+    return Impl::getHashValue((uint8_t)Val);
+  }
+  static bool isEqual(const KnownProtocolKind &LHS,
+                      const KnownProtocolKind &RHS) {
+    return LHS == RHS;
+  }
+};
+} // namespace llvm
+
 #endif