Fix "previously declared as a struct" warning

clang/include/clang/AST/ASTContext.h

@@ -116,7 +116,7 @@ class ObjCPropertyDecl;
 class ObjCPropertyImplDecl;
 class ObjCProtocolDecl;
 class ObjCTypeParamDecl;
-struct OMPTraitInfo;
+class OMPTraitInfo;
 struct ParsedTargetAttr;
 class Preprocessor;
 class Stmt;

clang/include/clang/Serialization/ASTRecordReader.h

@@ -22,7 +22,7 @@
 #include "llvm/ADT/APSInt.h"
 
 namespace clang {
-struct OMPTraitInfo;
+class OMPTraitInfo;
 
 /// An object for streaming information from a record.
 class ASTRecordReader