X64: Fix error in Win64 platform specific code in regexp stub.

src/x64/code-stubs-x64.cc

 // Copyright 2011 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 2627 matching lines @@
   __ bind(&setup_two_byte);
   __ SmiToInteger32(rcx, FieldOperand(rdi, String::kLengthOffset));
   __ lea(arg4, FieldOperand(rdi, rcx, times_2, SeqTwoByteString::kHeaderSize));
   __ lea(arg3, FieldOperand(rdi, rbx, times_2, SeqTwoByteString::kHeaderSize));
 
   __ bind(&setup_rest);
   // Argument 2: Previous index.
   __ movq(arg2, rbx);
 
   // Argument 1: Subject string.
-#ifdef WIN64_
+#ifdef _WIN64
   __ movq(arg1, rdi);
 #else
   // Already there in AMD64 calling convention.
   ASSERT(arg1.is(rdi));
 #endif
 
   // Locate the code entry and call it.
   __ addq(r11, Immediate(Code::kHeaderSize - kHeapObjectTag));
   __ call(r11);
 
@@ skipping 2482 matching lines @@
           FieldOperand(elements, PixelArray::kExternalPointerOffset));
   __ movb(Operand(external_pointer, untagged_key, times_1, 0), untagged_value);
   __ ret(0);  // Return value in eax.
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64