[gn] Enable stricter build flags

src/lookup.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/lookup.h"
 
 #include "src/bootstrapper.h"
 #include "src/deoptimizer.h"
 #include "src/elements.h"
 #include "src/field-type.h"
@@ skipping 90 matching lines @@
     state_ = LookupInHolder<is_element>(map, holder);
   } while (!IsFound());
 
   holder_ = handle(holder, isolate_);
 }
 
 template <bool is_element>
 void LookupIterator::RestartInternal(InterceptorState interceptor_state) {
   interceptor_state_ = interceptor_state;
   property_details_ = PropertyDetails::Empty();
-  number_ = DescriptorArray::kNotFound;
+  number_ = static_cast<uint32_t>(DescriptorArray::kNotFound);
   Start<is_element>();
 }
 
 template void LookupIterator::RestartInternal<true>(InterceptorState);
 template void LookupIterator::RestartInternal<false>(InterceptorState);
 
 // static
 Handle<JSReceiver> LookupIterator::GetRootForNonJSReceiver(
     Isolate* isolate, Handle<Object> receiver, uint32_t index) {
   // Strings are the only objects with properties (only elements) directly on
@@ skipping 814 matching lines @@
 
   // We have found a cached property! Modify the iterator accordingly.
   name_ = maybe_name.ToHandleChecked();
   Restart();
   CHECK_EQ(state(), LookupIterator::DATA);
   return true;
 }
 
 }  // namespace internal
 }  // namespace v8