Fix compilation with recent MinGW64 versions.

src/preparser.h

 // 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 86 matching lines @@
 
   i::UnicodeCache* unicode_constants_;
   // Backing store used to store strings used as hashmap keys.
   i::SequenceCollector<unsigned char> backing_store_;
   i::HashMap map_;
   // Buffer used for string->number->canonical string conversions.
   char number_buffer_[kBufferSize];
 };
 
 
-#ifdef WIN32
-#undef Yield
-#endif
-
-
 class PreParser {
  public:
   enum PreParseResult {
     kPreParseStackOverflow,
     kPreParseSuccess
   };
 
 
   PreParser(i::Scanner* scanner,
             i::ParserRecorder* log,
@@ skipping 566 matching lines @@
   bool stack_overflow_;
   bool allow_lazy_;
   bool allow_natives_syntax_;
   bool allow_generators_;
   bool allow_for_of_;
   bool parenthesized_function_;
 };
 } }  // v8::preparser
 
 #endif  // V8_PREPARSER_H