Fix -Wsign-compare warnings in parser, scanner, regexp, runtime.

src/builtins/builtins-string.cc

 // Copyright 2016 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/builtins/builtins.h"
 #include "src/builtins/builtins-utils.h"
 
 #include "src/code-factory.h"
 #include "src/regexp/regexp-utils.h"
 
@@ skipping 583 matching lines @@
   }
 
   if (index == length) {
     RETURN_RESULT_OR_FAILURE(isolate, isolate->factory()->NewStringFromOneByte(
                                           one_byte_buffer.ToConstVector()));
   }
 
   List<uc16> two_byte_buffer(length - index);
 
   while (true) {
-    if (code <= unibrow::Utf16::kMaxNonSurrogateCharCode) {
+    if (code <= static_cast<uc32>(unibrow::Utf16::kMaxNonSurrogateCharCode)) {
       two_byte_buffer.Add(code);
     } else {
       two_byte_buffer.Add(unibrow::Utf16::LeadSurrogate(code));
       two_byte_buffer.Add(unibrow::Utf16::TrailSurrogate(code));
     }
 
     if (++index == length) {
       break;
     }
     code = NextCodePoint(isolate, args, index);
@@ skipping 812 matching lines @@
         Runtime::kThrowIncompatibleMethodReceiver, context,
         assembler->HeapConstant(assembler->factory()->NewStringFromAsciiChecked(
             "String Iterator.prototype.next", TENURED)),
         iterator);
     assembler->Return(result);  // Never reached.
   }
 }
 
 }  // namespace internal
 }  // namespace v8