Fix warnings on Win64.

src/x64/assembler-x64.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // 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.
 //
@@ skipping 1113 matching lines @@
   void RecordJSReturn();
 
   // Record a comment relocation entry that can be used by a disassembler.
   // Use --debug_code to enable.
   void RecordComment(const char* msg);
 
   void RecordPosition(int pos);
   void RecordStatementPosition(int pos);
   void WriteRecordedPositions();
 
-  int pc_offset() const  { return pc_ - buffer_; }
+  int pc_offset() const  { return static_cast<int>(pc_ - buffer_); }
   int current_statement_position() const { return current_statement_position_; }
   int current_position() const  { return current_position_; }
 
   // Check if there is less than kGap bytes available in the buffer.
   // If this is the case, we need to grow the buffer before emitting
   // an instruction or relocation information.
   inline bool buffer_overflow() const {
     return pc_ >= reloc_info_writer.pos() - kGap;
   }
 
   // Get the number of bytes available in the buffer.
-  inline int available_space() const { return reloc_info_writer.pos() - pc_; }
+  inline int available_space() const {
+    return static_cast<int>(reloc_info_writer.pos() - pc_);
+  }
 
   // Avoid overflows for displacements etc.
   static const int kMaximalBufferSize = 512*MB;
   static const int kMinimalBufferSize = 4*KB;
 
  protected:
   // void movsd(XMMRegister dst, const Operand& src);
   // void movsd(const Operand& dst, XMMRegister src);
 
   // void emit_sse_operand(XMMRegister reg, const Operand& adr);
@@ skipping 230 matching lines @@
  private:
   Assembler* assembler_;
 #ifdef DEBUG
   int space_before_;
 #endif
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_ASSEMBLER_X64_H_