Fix cast warning on Win32

src/ia32/code-stubs-ia32.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 6895 matching lines @@
   // types loaded in tmp1 and tmp2.
   STATIC_ASSERT(kInternalizedTag != 0);
   __ mov(tmp1, FieldOperand(left, HeapObject::kMapOffset));
   __ mov(tmp2, FieldOperand(right, HeapObject::kMapOffset));
   __ movzx_b(tmp1, FieldOperand(tmp1, Map::kInstanceTypeOffset));
   __ movzx_b(tmp2, FieldOperand(tmp2, Map::kInstanceTypeOffset));
 
   Label succeed1;
   __ test(tmp1, Immediate(kIsInternalizedMask));
   __ j(not_zero, &succeed1);
-  __ cmpb(tmp1, static_cast<int8_t>(SYMBOL_TYPE));
+  __ cmpb(tmp1, static_cast<uint8_t>(SYMBOL_TYPE));
   __ j(not_equal, &miss);
   __ bind(&succeed1);
 
   Label succeed2;
   __ test(tmp2, Immediate(kIsInternalizedMask));
   __ j(not_zero, &succeed2);
-  __ cmpb(tmp2, static_cast<int8_t>(SYMBOL_TYPE));
+  __ cmpb(tmp2, static_cast<uint8_t>(SYMBOL_TYPE));
   __ j(not_equal, &miss);
   __ bind(&succeed2);
 
   // Unique names are compared by identity.
   Label done;
   __ cmp(left, right);
   // Make sure eax is non-zero. At this point input operands are
   // guaranteed to be non-zero.
   ASSERT(right.is(eax));
   __ j(not_equal, &done, Label::kNear);
@@ skipping 804 matching lines @@
   // Restore ecx.
   __ pop(ecx);
   __ ret(0);
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32