Fix Windows build.

src/ia32/codegen-ia32.cc

 // Copyright 2006-2009 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 2190 matching lines @@
         Label comparison;
         // If the length is 0 then our subtraction gave -1 which compares less
         // than any character.
         __ j(negative, &comparison);
         // Otherwise load the first character.
         __ movzx_b(temp2.reg(),
                    FieldOperand(left_side.reg(), SeqAsciiString::kHeaderSize));
         __ bind(&comparison);
         // Compare the first character of the string with out constant
         // 1-character string.
-        __ cmp(Operand(temp2.reg()),
-               Immediate(String::cast(*right_side.handle())->Get(0)));
+        uint8_t char_value =
+            static_cast<uint8_t>(String::cast(*right_side.handle())->Get(0));
+        __ cmp(Operand(temp2.reg()), Immediate(char_value));
         Label characters_were_different;
         __ j(not_equal, &characters_were_different);
         // If the first character is the same then the long string sorts after
         // the short one.
         __ cmp(FieldOperand(left_side.reg(), String::kLengthOffset),
                Immediate(1));
         __ bind(&characters_were_different);
       }
       temp2.Unuse();
       left_side.Unuse();
@@ skipping 7352 matching lines @@
   __ ret(3 * kPointerSize);
 
   // Just jump to runtime to create the sub string.
   __ bind(&runtime);
   __ TailCallRuntime(ExternalReference(Runtime::kSubString), 3, 1);
 }
 
 #undef __
 
 } }  // namespace v8::internal