Fix compilation with recent MinGW64 versions.

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

 // Copyright 2012 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 743 matching lines @@
   __ neg(rbx);
   if (mode_ == UC16) {
     __ lea(rax, Operand(rdi, rbx, times_2, -char_size()));
   } else {
     __ lea(rax, Operand(rdi, rbx, times_1, -char_size()));
   }
   // Store this value in a local variable, for use when clearing
   // position registers.
   __ movq(Operand(rbp, kInputStartMinusOne), rax);
 
-#ifdef WIN32
+#if V8_OS_WIN
   // Ensure that we have written to each stack page, in order. Skipping a page
   // on Windows can cause segmentation faults. Assuming page size is 4k.
   const int kPageSize = 4096;
   const int kRegistersPerPage = kPageSize / kPointerSize;
   for (int i = num_saved_registers_ + kRegistersPerPage - 1;
       i < num_registers_;
       i += kRegistersPerPage) {
     __ movq(register_location(i), rax);  // One write every page.
   }
-#endif  // WIN32
+#endif  // V8_OS_WIN
 
   // Initialize code object pointer.
   __ Move(code_object_pointer(), masm_.CodeObject());
 
   Label load_char_start_regexp, start_regexp;
   // Load newline if index is at start, previous character otherwise.
   __ cmpl(Operand(rbp, kStartIndex), Immediate(0));
   __ j(not_equal, &load_char_start_regexp, Label::kNear);
   __ Set(current_character(), '\n');
   __ jmp(&start_regexp, Label::kNear);
@@ skipping 655 matching lines @@
   }
 }
 
 #undef __
 
 #endif  // V8_INTERPRETED_REGEXP
 
 }}  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64