Move regexp implementation into its own folder.

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_INTERPRETER_IRREGEXP_H_
-#define V8_INTERPRETER_IRREGEXP_H_
+#ifndef V8_REGEXP_INTERPRETER_IRREGEXP_H_
+#define V8_REGEXP_INTERPRETER_IRREGEXP_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 v8::internal
 
-#endif  // V8_INTERPRETER_IRREGEXP_H_
+#endif  // V8_REGEXP_INTERPRETER_IRREGEXP_H_