Fix warnings on Win64.

src/x64/regexp-macro-assembler-x64.cc

 // Copyright 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 1061 matching lines @@
 
   // Find the current start address of the same character at the current string
   // position.
   int start_index = frame_entry<int>(re_frame, kStartIndex);
   const byte* new_address = StringCharacterPosition(*subject, start_index);
 
   if (start_address != new_address) {
     // If there is a difference, update the object pointer and start and end
     // addresses in the RegExp stack frame to match the new value.
     const byte* end_address = frame_entry<const byte* >(re_frame, kInputEnd);
-    int byte_length = end_address - start_address;
+    int byte_length = static_cast<int>(end_address - start_address);
     frame_entry<const String*>(re_frame, kInputString) = *subject;
     frame_entry<const byte*>(re_frame, kInputStart) = new_address;
     frame_entry<const byte*>(re_frame, kInputEnd) = new_address + byte_length;
   }
 
   return 0;
 }
 
 
 Operand RegExpMacroAssemblerX64::register_location(int register_index) {
@@ skipping 190 matching lines @@
                  Operand(rsi, rdi, times_1, cp_offset * sizeof(uc16)));
     }
   }
 }
 
 #undef __
 
 #endif  // V8_NATIVE_REGEXP
 
 }}  // namespace v8::internal