Fixed some undefined behavior in our external header.

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index e3cd10fa8d690cca9ddf4ed5b8fdbc4a1f366f67..2eaae7d49de4a847a4ae6f092bdec0d7deadc953 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -5599,8 +5599,8 @@ template <size_t ptr_size> struct SmiTagging;
 template<int kSmiShiftSize>
 V8_INLINE internal::Object* IntToSmi(int value) {
   int smi_shift_bits = kSmiTagSize + kSmiShiftSize;
-  intptr_t tagged_value =
-      (static_cast<intptr_t>(value) << smi_shift_bits) | kSmiTag;
+  uintptr_t tagged_value =
+      (static_cast<uintptr_t>(value) << smi_shift_bits) | kSmiTag;
   return reinterpret_cast<internal::Object*>(tagged_value);
 }
 
@@ -5770,7 +5770,7 @@ class Internals {
   V8_INLINE static void UpdateNodeFlag(internal::Object** obj,
                                        bool value, int shift) {
       uint8_t* addr = reinterpret_cast<uint8_t*>(obj) + kNodeFlagsOffset;
-      uint8_t mask = static_cast<uint8_t>(1 << shift);
+      uint8_t mask = static_cast<uint8_t>(1U << shift);
       *addr = static_cast<uint8_t>((*addr & ~mask) | (value << shift));
   }