do not redefine a typedef

duplicated typedef declaration was not allowed in C99.

internal/ruby_parser.h

@@ -1,8 +1,9 @@
 #ifndef INTERNAL_RUBY_PARSE_H
 #define INTERNAL_RUBY_PARSE_H
 
-#include "rubyparser.h"
 #include "internal.h"
+#include "internal/imemo.h"
+#include "rubyparser.h"
 #include "vm.h"
 
 RUBY_SYMBOL_EXPORT_BEGIN

rubyparser.h

@@ -327,8 +327,11 @@ typedef struct rb_ast_struct {
  * Parser Interface
  */
 
+
 typedef struct parser_params rb_parser_t;
+#ifndef INTERNAL_IMEMO_H
 typedef struct rb_imemo_tmpbuf_struct rb_imemo_tmpbuf_t;
+#endif
 
 #ifdef UNIVERSAL_PARSER
 typedef struct rb_parser_config_struct {