[clang][NFC] Annotate RawCommentList.h with preferred_type

Author: Endilll

clang/include/clang/AST/RawCommentList.h

@@ -178,6 +178,7 @@ class RawComment {
   mutable bool RawTextValid : 1;   ///< True if RawText is valid
   mutable bool BriefTextValid : 1; ///< True if BriefText is valid
 
+  LLVM_PREFERRED_TYPE(CommentKind)
   unsigned Kind : 3;
 
   /// True if comment is attached to a declaration in ASTContext.