[regexp] do not include irregexp interpreter by default.

src/regexp/interpreter-irregexp.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // A simple interpreter for the Irregexp byte code.
 
 #ifndef V8_REGEXP_INTERPRETER_IRREGEXP_H_
 #define V8_REGEXP_INTERPRETER_IRREGEXP_H_
 
+#ifdef V8_INTERPRETED_REGEXP
+
 #include "src/regexp/jsregexp.h"
 
 namespace v8 {
 namespace internal {
 
-
 class IrregexpInterpreter {
  public:
   static RegExpImpl::IrregexpResult Match(Isolate* isolate,
                                           Handle<ByteArray> code,
                                           Handle<String> subject,
                                           int* captures,
                                           int start_position);
 };
 
 
 }  // namespace internal
 }  // namespace v8
 
+#endif  // V8_INTERPRETED_REGEXP
+
 #endif  // V8_REGEXP_INTERPRETER_IRREGEXP_H_