Fix a nit

Author: Fznamznon

clang/lib/Sema/HLSLExternalSemaSource.cpp

@@ -546,8 +546,9 @@ struct BuiltinTypeMethodBuilder {
 public:
   ~BuiltinTypeMethodBuilder() { finalizeMethod(); }
 
-  BuiltinTypeMethodBuilder(BuiltinTypeMethodBuilder &Other) = delete;
-  BuiltinTypeMethodBuilder &operator=(BuiltinTypeMethodBuilder &Other) = delete;
+  BuiltinTypeMethodBuilder(const BuiltinTypeMethodBuilder &Other) = delete;
+  BuiltinTypeMethodBuilder &
+  operator=(const BuiltinTypeMethodBuilder &Other) = delete;
 
   Expr *getResourceHandleExpr() {
     // The first statement added to a method or access to 'this' creates the